Introduction to Procedural Programming in C++

Introduction to Procedural
Programming
Department of Software Engineering
College of Engineering
University of Salahaddin
Erbil

1

About this Course
in this course, we will be learning to write procedural* programs.
The main tool needed for writing programs is a programming
language.
Because of the popularity of C++ in the academic world and
business, and its standardization, we will use C++ as our
programming language.

C++ as a programming language is very powerful and feature-rich. it
is a general-purpose programming language that can be used for
many different situations. it can be used to write low-level system
programs or high-level programs.
*This term will be explained later.

introduction to Procedural Programming

2

About this Course, cont
C++ supports both procedural programming and object-oriented
programming. in this course, this year, we will concentrate on
procedural programming in C++. Next year, we will cover objectoriented aspects of the language.
We will begin the study of the language starting with the
fundamentals of the language and simple programs; and as we
explore more of the language, we will write increasingly larger
programs.
By the end of this year, every student:
• will learn about all the essential programming concepts
• will demonstrate a good familiarity with C++ syntax
• will be able to write reasonably complex procedural programs

3

Programming
Programming is about solving problems. Most often, a programmer,
or a group of programmers, is presented with a problem and asked
to produce a computerized solution for that problem.
Almost anything that a computer can do, a human can also do. So
why do we need computers and programs to solve our problems???
The basic reason is that humans are not good at doing repetitive
jobs while computers ARE. Humans can perform a few calculations
and get tired(especially if the calculations are long and complex).
Computers hardly get tired. in a perfect world, a computer could
carry out endless repetitive and long calculations without stop.
Another reason is that computers are much faster at performing
calculations than humans. Modern computers can carry out millions
Of basic instructions per second.

4

Good Programming
Programming is a challenge. Often, programs are late, difficult to
use,full of bugs, un-maintainable, and wrong. When someone writes
a program, they should not only think about the people who will use it,
but also about the people who will maintain it.
Writing good programs comes only after a lot of practice and
experience. Good programs are programs that are:






on time
‘user-friendly’
reliable and stable
maintainable and extensible
correct (do what they were intended to do)


5

Good Programming, cont
To be able to write effective programs, one needs to know a few
things:
 mastery of the tools-of-the-trade(programming language,
development environment etc.)
 the ability to analyze a ‘real world’ problem and to construct
a model for it suitable for programming
 careful design of an algorithm and user-interface for the
program at hand
 knowing the techniques that have made other programmers
more effective, and a reluctance to reinvent the wheel!
 Practice and exercise


6

The Syllabus
The following topics will be covered in this course:
• introduction
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variables and assignment
input, output (i/O), formatting output
basic data types
a simple C++ program
arithmetic operators
flow of control and loops
program style
procedures and functions
references
local and global variables, constants
procedural abstraction
file i/O
character i/O
structures and arrays
numerical analysis(Electrical Engineering only)
recursion


7

Variables
A C++ variable is a placeholder used for storing data. The type of
data may be numerical, string, character and any other type that
the language supports. We will study all the data types in C++ later
in the course.
The data in a variable is called its value and it can be changed or
deleted.
in order to uniquely identify and keep track of a variable, we need
to give each variable a name; this is called declaring a variable. it is
a good idea to use meaningful names for variables. For example:
int books;

in this variable declaration, we declare a variable named “books”
to be of type int (int is short for integer which refers to whole
numbers like 1,5,192 etc.)

8

Variables, cont
in the example on the previous page, we want the variable “books”
to hold the number of books in a program.
Also note that here, we used the data type int which represents
whole numbers. We used this data type because the number of
books is a whole number like 17 and not 3.6, for example. The data
type of numerical values with decimals is called double. We will
cover all data types later. For now keep it in mind that whole
numbers are of type int and decimal numbers of type double.
double myWeight;

in this case, the variable myWeight is of type double because its
value can be a number with a fraction like 1.3.
Note that all variable declarations end with a semicolon(;).

9

Variables, cont
To be more specific, a variable is a memory location which
can contain a value of some type. A variable declaration like
int books

first maps a name(books) to a memory location in the computer’s
memory and tells the computer what type of data will be stored in
this variable. A variable must be declared before it can be used.
when the name of a variable appears in a program, its value is
obtained.
it’s common to initialize variables upon declaration. if a variable
is used in a program without being initialized, the results will
be unpredictable. Variable initialization can be performed either
during declaration using assignment statements (to be discussed
shortly) as in
int books=0;

Or using the input statement cin (input will be discussed later).

10

Assignment Statements
Values can be assigned or stored in variables with assignment
statements:
books=34;

An assignment statement is an order, to the computer, to assign
the value on the right-hand side of the equal sign to the variable on
the left-hand side. The sign (=) is called the assignment operator.
(C++ operators will be covered later in the course). Assignment
statements end with a semicolon.
The value on the right-hand side can also be another variable or
expression:
books1=books2;

in an assignment statement, first the value on the right-hand side
is evaluated and then its result is stored or assigned to the variable
on the left-hand side.

11

Performing Output
The values of variables, numerical values and strings of text ,may be
output to the screen using cout as in
int books=0;
cout<<books<<endl;
cout<<72<<endl;
cout<<“This is the output”<<endl;

in the first output statement, the value of variable books will be
output on the screen, which is 0;
in the second, the numerical value 72 will be output to the screen,
and in the last statement, the string “This is the output” will be
output to the screen.


12

Performing output, cont
Typically, you would want a new line to appear after some output to
the screen; to force a new line the C++ keyword endl is appended at
the end of the line. A second method for forcing a new line is using
the escape character n as in:
cout<<“Hello everyonen”;

But this is only possible when the output is a text of string.
You can also combine a number of outputs in a single output
statement as in
cout<<“i am “<<18<<“years old”<<endl;

To force a blank line on the screen use either
cout<<endl; or cout<<“n”;

The double arrow signs (<<) are called the insertion operators.

13

Formatting Output
When the computer outputs a value of type double, the format may
not be what you would expect. Eg, if double price=78.5;
might output:

cout<<“The price is $”<<price<<endl;

The price is $78.500000
or
The price is $78.5
or
The price is $7.850000e01
But, it is unlikely that the output will be
The price is $78.50
which is the format that is most common for currency.
To specify the number of decimal point in values of type double we
Use the following formula before the above statement:
cout.setf(ios::fixed);
cout.setf(ios::showpoint)

(will output $78.50)

cout.precision(2);

14

input using cin
in C++, cin is used to input values into variables. After declaring a
variable of type int,
int price;
cout<<“Enter the price:”;
cin>>price;
cout<<“The price you entered is $“<<price<<endl;

in this program extract, first an integer is declared, then the user
is asked to enter/type a value for price. This value is then input in
the variable price using cin. A message is also output to the screen
notifying the user of the input value.
When the program reaches a cin statement, it waits for input to be
entered from the keyboard and for this value to be input into the
Variable, the user must enter a new line.

15

input using cin, cont
To have more than one input value entered at the keyboard, use
more variables to store the inputted values as in
int price1,price2;
(two variables of type int)
cout<<“Enter two prices:”<<endl;
cin>>price1>>price2;

Or you could have two separate cin statements. After each input,
the computer waits for user to input some value. Then the user must
type a space or a tab or a new line to separate the two
input values.
The double arrows of cin statements are the same as for output
statements (cout) except they are in the opposite direction. A cin
statement sets the value of a variable equal to values typed at
the keyboard.

16

Basic Data Types
integer Numbers (int)
As we have already mentioned the type int refers to whole numbers
like 37 and –45. The range of numbers of type int is usually between
-2,147,483,647 and 2,147,483,647 (4 bytes are used to store the
number) But this is system-dependent and some systems support
bigger ranges.
Real Numbers(Double)
And we also pointed out that numbers with fractional parts such as
3.56 and 0.112 are of type double.(the real numbers in mathematics).
For numbers of type double the range is between 1.7E + 308 and
1.7E - 308. Here, the number 1.7E + 308 is equal to 1.7 multiplied by
10 to the power of 308. 1.7 x 10308. This is called the scientific
notation. (8 bytes are used to store double numbers). Numbers of
type double can have a precision of up to 15 digits.

17

Basic Data Types, cont
We have seen two numeric types that the C++ supports: double and
int types. These two are the main numeric types in C++. You can
use these types for almost any situation. However, C++ includes
Memory Used Size Range
Precision
other numeric types Type
short or
2 bytes
-32,767 to 32,767
N/A
which are derived
short int
and based on these
int
4 bytes
-2,147,483,647 to
N/A
two types. These
2,147,483,647
types allow for difflong or
4 bytes
-2,147,483,647 to
N/A
erent number sizes
long int
2,147,483,647
and for more or less float
4 bytes
Approximately
7 digits
precision.
10-38 to 1038
Also can be used to
make more efficient
use of the memory.

double

8 bytes

Approximately

15 digits

10-308 to 10308
long double


10 bytes

Approximately
10-4932 to 104932

18

19 digits

Characters (char)
Computers and C++ not only use numerical values but they can also
use non-numerical values like characters and strings. Values of type
char include letters of the alphabet, digits, symbols and punctuation
marks. For example:
char letter, symbol;
letter=‘A’;
symbol=‘#’;
Notice that character values are placed inside single quotes. We
have already seen the string data type where the string of text is
Placed inside double quotes as in:
cout<<“This is string of text.”<<endl;
So, in C++ the character ‘A’ is treated differently from “A” since
the first is considered a character and the second a string.

19

String data types will be discussed later. For now, we just use
values of Type string to output text onto the screen using C++
cout statements.
Let’s look at a small program extract using char and string types:
char letter;
cout<<“Enter a letter: “;
cin>>letter;
cout<<“You typed the letter: “<<letter<<endl;
Here, we first declare a char variable and ask the user to type a
letter. After typing a letter and pressing the Enter key, the value
is stored in the variable letter using cin statement. Then, the user
is notified about the value that he/she typed.
The variable letter is of type char, while the text string Enter a
Letter is of type string ( string or sequence of characters).

20

Boolean expressions (bool)
The last basic data type we will look at is called bool. This type was
recently added to the language.
Values of type bool are called Boolean expressions and include only
two values: true or false. Boolean expressions are used in branching
And looping statement which we will cover later in the course.
important note
As a general rule, you cannot store values of one type in a variable of
another type. This is a good rule to follow, even though some C++
compilers do not enforce this type checking.

21

A simple C++ Program
Now, we will write our first complete C++ program.
#include <iostream.h>
main()
{
int hours=0;
cout<<“This is your first C++ program”<<endl;
cout<<“Welcome to C++ Programming”<<endl;
cout<<endl<<endl;
cout<<“How many hours/week do you practice C++ ?”;
cin>>hours;
cout<<“You practice “<<hours<<“ per week.”<<endl;
cout<<“OK, this is enough for now.”<<endl;
return 0;
}
in the next slide, we will dissect this program line by line.

22

Program Dissection
Line 1:
This include statement directs the C++ compiler to include the
iostream.h library file with the program. This library contains input/
output function definitions of the C++ language cin and cout. Without
including this library file, you cannot use cin/cout for input/output.
We will use other C++ libraries later.
You can even write your own libraries and include them in your C++
programs. We will see this later.
Line 2:
Every C++ program must have a function called main. This function
has a body consisting of program statements to be executed in
sequence by the computer. (See next slide)

23

Program Skeleton
The skeleton of a typical C++ program is as follows:
#include library1
#include library2
.
.
.
function prototypes;
main()
{
statement1;
statement2;
.
.
.
return 0;
}
function definitions;

24

Program Dissection, cont
Lines 3, 13:
Every main function starts with an open bracket { and ends with a
close bracket }.
Line 4:
in this line we declare and initialize a variable of type int.
Lines 5,6,8,11
Here, we are just outputting some text to the screen.
Line 7:
We output two blank lines onto the screen for clarity.
Line 9:
We capture the user input value and store it in a variable.

25

Program Dissection, cont
Line 10:
in this line, we output some text and a the value of the variable
hours.
Line 12:
Here, at the end of the program, we return control to the operating
system and declare that the program has finished its execution.

important Note
The important thing to remember is that all C++ programs must have
a function called main and that program execution begins and ends
inside this function.

26

Arithmetic Operators
in C++, you can combine expressions using the arithmetic operators.
Usually, arithmetic operators come in between two expressions as in
expression1

Or

operand1

operator expression2
operator opreand2

The operand can be either a single variable/number or a composite
expression.
The main C++ arithmetic operator are the following:
+
for addition
for subtraction
*
for multiplication
/
for division
%
for division remainder

27

Arithmetic Operators, cont
For example:
int number_of_computers=10;
int price_of_computer=7340;
int total_price=price_of_computer * number_of_computers;
operand1

operator

operand2

All of the arithmetic operators can be used with numbers of type int,
numbers of type double and even with one number of each type.
Division Operator (/)
However, if both operands are are of type int, the result is of type int.
if one, or both operands are of type double, the result will be of type
double.

28

Arithmetic Operators, cont
When used with one or both operands of type double, the division
Operator, /, behaves as you would expect: 10/4.0=2.5
But when used with two operands of type int, the division operator /
gives only the integer part of the division: 10/3 is 3 and not 3.333…
Remainder Operator (%)
The % operator can be used with operands of type int to recover
the information lost when you use / to do division with operands of
type int; for example:
cout<<“11 divided by 3 is “<<11/3<<endl;
cout<<“with a remainder of “<<11%3<<endl;
Output:

11 divided by 3 is 3
with a remainder of 2


29

Precedence Rules
You can specify the order of operations in C++ using parentheses as
illustrated in the following expressions:
1:
(x + y) * z
2:
x + (y * z)
1: the computer first adds x to y and then multiplies the result by z.
2: the computer first multiplies y by z and then adds the result to x.
if you omit the parentheses, the computer will follow the C++ rules
of precedence. So, if you wrote x + y * z, the computer would
multiply y by z and add the result to x. Because * has higher
precedence than + .(the same is true for / and %)
it’s always best to use parentheses as they remove any ambiguity
and make the code much clearer to read and understand.

30

More Assignment Statements
C++ has shorthand notation that combines the assignment operator
(=) and an arithmetic operator. For example:
int hours=5;
hours += 7; is equivalent to

hours=hours + 7;

That is, the new value of the variable hours is equal to its old value
plus the number constant 7.
We can use other arithmetic operators too:
hours -=2;
hours /=3;
hours *=2;
hours %=8;

hours=hours-2;
hours=hours/3;
hours=hours*2;
hours=hours%8;

31

Flow of Control
in the simple C++ program we saw earlier, the program consisted of
a list of program statements which were executed sequentially; one
statement after another. There we did not specify any order for
the program to follow.
For bigger and more sophisticated programs, you will need some way
to vary the order in which statements are executed. The order in
which statements are executed is called the flow of control.
C++ has a number of mechanisms which let you control the flow of
program execution.
First, we will study a branching mechanism that allows you to choose
between two alternative actions. Then we will discuss loops.


32

Branching (if-else statement)
There is a C++ statement that chooses between two alternative
actions. it is called the if-else statement. in fact, there are two
versions of this statement. We will discuss the first one as the
second form is an extension of the first form.
The general form of the if-else-statement is as follows:

if (Boolean-expression)
yes-statement
else
no-statement
When program execution reaches the if-else-statement only one
of the two statements is executed, not both. if the Boolean-expression is true then the yes-statement is executed. if the the
Boolean-expression is false then the no-statement is executed.

33

Branching (if-else statement), cont
Example:
Suppose your program asks the user about the amount of time per
week he/she spends on practicing C++. And you want the program
to decide whether or not this is enough. Assume that 4 hours/week
of practice is enough. Anything less is not good enough.
main()
{
int hours_per_week=0;
cout<<“How many hours/week do you practice C++? “<<endl;
cin>> hours_per_week;
if (hours_per_week>=4)
cout<<“That’s good ”<<endl;
else
cout<<“That’s not good enough”<<endl;
return 0;
}

34

Branching (if-else statement), cont
The Boolean expression in the if-else-statement is:
hours_per_week>=4
Remember that Boolean expressions or variables have only 2 values:
true and false. C++ checks whether this Boolean expression is true
or false by comparing the value of the variable and the constant 4.
Here, we use C++ comparison operators. Here is the full list of
comparison operators:
Math Symbol

C++ Notation

Description

=

==

Equal to

≠

!=

Not equal to

<

<

Less than

≤

<=

Less than or equal
to

>

>

Greater than

⋝

>=

Greater than or
equal to


35

Boolean Logic
in evaluating Boolean expressions, C++ uses Boolean Logic principles.
You can combine two (or more) comparisons using the Boolean Logic
“and” operator. For example, the expression
(x>2) && (x <10)
is true only if both (x>2) and (x<10) Boolean expressions are true.
To remind you of the Boolean Logic truth tables:
X

Y

X || Y

True

True

True

True

False

True

False

True

True

False

False

False

X

Y

X &&
Y

True

True

True

True

False

False

False

True

False

False

False

False

Note: && is equivalent to “and” and || to “or”.

36

if-else-statement, cont
Sometime, you want your program to test a condition and if the
condition is satisfied the program does something, otherwise it does
not do anything. You can do this by omitting the else part from the
if-else-statement. For example:
if (grade>=50)
cout<<“The student has passed.”<<endl;
cout<<“……”<<endl;
So, if the Boolean expression is not satisfied, the cout statement
will not be executed and program execution will go to the second
cout line.
This is called the if-statement, as opposed to if-else-statement.

37

if-else-statement, cont
You may want to execute more than one statement inside an if-elsestatement. To do this, enclose the statements inside brackets { }.
For example:
if (grade >=50)
{
cout<<“ The student has passed”<<endl;
passed-students +=1;
}
else
{
cout<<“Student has failed”<<endl;
failed-students +=1;
}

A list of statements enclosed inside brackets is called a compound
statement.

38

Loops
Most programs have some action that is repeated a number of times.
A section of a program repeats a statement or group of statements
is called a loop. C++ has a number of ways to create loops. One of
them is called a
main()
while-statement or
{
while-loop.
int num_of_greetings=0;
cout<<“How many greetings do you want? ” ;
cin>>num_of_greetings;

}

while (num_of_greetings > 0)
{
cout<<“Hello “;
num_of_greetings=num_of_greetings-1;
}
return 0;


Boolean expression

39

Loops, cont
in the example on the previous page, the section between the
brackets { and } is called the body of the while-loop. it is the action
that is repeated a number of times. Each repetition of the loop is
called an iteration of the loop.
if the user enters 0 at the keyboard, the loop body is executed zero
times, that is, it is not executed at all. Because, the Boolean-exp
is not satisfied and program execution proceeds with the following
line after the while-loop.
Note that you need some way to make sure that the loop ends at
some point. Otherwise, the loop will run for ever. in this example,
we decrease a variable value after each iteration. We decrease it
by one after each iteration. This is called decrementing.

40

increment and Decrement Operators
We have already seen a number of binary operators such as * and /.
They were called binary because they take two operands, one on
their left and one on their right.
Unary operators have only one operand. You know unary operators
+ and –, in +8 and –9. The C++ language has two more unary operators
++ and --. The ++ operator is called the increment operator and -the decrement operator. They are usually used in variables of type
int. The operator ++ increases a variable’s value by one and –
decreases a variable’s value by one. Example:
int count=5;
count++;
cout<<“Count is changed to “<<count<<endl;
count--;
cout<<“Count is changed to “<<count<<endl;

41

Loops, cont
As you know, a while-loop might execute its loop body zero times. if
you know that under all circumstances your loop body should be
executed at least one time, then you can use a do-while loop statement. The do-while loop statement is similar to the while-loop statement, except that the loop body is executed at least once. The syntax
of do-while loop statements is as follows:
do
{
Statement_1;
Statement_2;
…
Statement_n;
} while (Boolean-expression);

Loop body is executed once first, then the Boolean expression is
checked for additional iterations of the loop body.

42

Loops, cont
An example involving a do-while loop statement:
main()
{
char answer=‘n’;
do
{
cout<<“Hellon”;
cout<<Do you want another greeting?n”
<<“Press y for yes, n for no,n”
<<“and then press Enter/Return: “;
cin>>answer;
} while (answer ==‘y’ || answer == ‘n’);
cout<<“Goodbyen”;
}

43

infinite Loops (Be Careful)
A while-loop or do-while loop does not terminate as long as the Boolean expression is true.
This Boolean expression normally contains
a variable that will be changed by the loop body and usually the value
of this variable eventually is changed in a way that makes the Boolean expression false and therefore terminates the loop.
However if you make a mistake and write your program so that the
Boolean expression is always true, then the loop will run forever. (an
infinite loop).
On the next page we will write two loops, one that does terminate
and one that does not terminate.

44

infinite Loops, cont
Write positive even numbers less than 12:
int x=2;
while ( x ! = 12)
{
cout<<x<<endl;
x=x+2;
}

Write positive odd numbers less than 12:
int x=1;
while ( x ! = 12)
{
cout<<x<<endl;
x=x+2;
}

Which is an infinite loop?
To terminate a program use control-C or Ctrl-C on the keyboard.

45

Program Style
All the variable names in our programs were chosen to suggest their
use. We tried to use meaningful names for variable names. Also we
laid out our programs in a particular format. For example, the
declarations and statement were all indented the same amount.
This is good programming as it makes our programs
• easier to read
easier to correct, and
•
easier to change
•
indenting
A program should be laid out so that elements that are naturally
Considered a group are made to look like a group. One way to do this
is to skip a line between parts that are logically considered separate.


46

Program Style, cont
indenting can help to make the structure of the program clearer. A
statement within a statement should be indented.
Also, the brackets {} determine a large part of the structure of a
program. Placing each on a separate line by itself, as we have been
doing, makes it easy to find the matching bracket.
One one pair of brackets is embedded inside another pair, the inner
pair should be indented more than the outer pair.
Comments
To make programs understandable, you should include some explanatory
notes at important places in the program. Such notes are called
comments. Most programming languages have this capability. in C++,
the symbols // are used to indicate start of a comment to the end
of the line. These comments can be as long as a line only.

47

Program Style
There is another way to insert comments in a C++ program. Anything
between /* and */ is considered a comment and ignored by the C++
compiler. Unlike the // comments, which require an additional // on
each new line, the /* to */ comments can span several lines.
Your programs should always start with some comments like:
//File name: hello.cpp
//Author: Mr. Nice
//Email: nice@microsoft.com
//Description: Program to output Hello World
//Last changed: 28 October 2000
Use comments sparingly; using two many comments is almost worse
than no comments at all!.


48

Constants
The word ‘variable’ means something that changes frequently. The
value of a variable may change several times in the program.
Sometimes it is required to have some value unchanged throughout
the program execution. Some value that does not change in a C++
program is called a constant. For example:
const int ENGiNEERiNG_AVERAGE=90;
if (student_grade >= ENGiNEERiNG_AVERAGE)
cout<<“Engineering Student”<<endl;
else
cout<<“Science Student”<<endl;

This could be a large program and there could be many places where
the constant engineering_average is used. To change eng. average
for next year, we only need to change the value at one place.
it’s common to use capital letters for constants.

49

Exercises
1.

What is the output of the following program fragment?
int x=10;
while (x > 0)
{
cout<<x<<endl;
x=x-3;
}

2. What output would be produced in the previous exercise if the >
sign were replaced by <?
3. Write a program fragment to have the same output as the
exercise 1 fragment but use a do-while loop this time.

50

Exercises, cont

4. What is the most important difference between a while-loop and
a do-while loop statement?

5. Write an if-else statement that outputs the word ‘High’ if the
Value of variable score is greater than 100 and ‘Low’ if the value of
score is at most 100. The variable score is of type int.

6. Consider a quadric expression such as:
x2 – x – 2
Describing where this quadratic is positive, involves finding
A set of numbers that are either less than the smaller root
(-1) or greater than the larger root (+2).
Write a C++ Boolean expression that s true when this equation
has positive values.

51

Exercises, cont
7. The following if-else statement will compile and run without any
Problems. However, it is not laid out in a way that is consistent with
the other if-else statements we have used in our programs. Rewrite
it so that the layout is clearer and similar to how we have been doing.
if (x < 0) { x=7; cout<<“x is now positive.”;} else
{ x =-7; cout<<“x is now negative.”;}

8. What is the output of the following program fragment?
//this is not a comment
/* cout<<“Hi”<<endl; does nothing
cout<<“Hi again”<<endl;
*/
cout<<“Hi again”<<endl; // this is a comment
/*this too is a comment*/

52

Exercises, cont
9. Write a program fragment to display the numbers that are
multiples of 4 between 0 and 20 inclusive.
10. Write a program to
1. Ask the user for two whole numbers (int)
2. Calculate their addition, subtraction, multiplication, division
and molulus
3. Display the results on the screen
10. Write a multiplication calculator program. This program will
multiply numbers together and display the result on the
screen. The program should keep asking the user for two
numbers until the user enters the letter ‘s’ for stop.

53

Exercises, cont

2. Write a program fragment to check the students grade and
coursework. if either the student’s maths grade is greater than 50
or the students physics grade is greater than 60 then the program will
output the word ‘Passed’ otherwise the word ‘Failed’.

3. Write a program fragment that reads in a year (Ex. 1972) and
checks whether or not this year is a leap year or not. Remember
a leap year is a year that has 366 days. To be a leap year, one of the
following conditions must hold:
1. The year is divisible by 4 but not by 100, or
2. The year is divisible by 400

4. Write a program to add a list of numbers entered by the user.
The user can stop the program by entering 0 when asked for the
next number. Before it stops, it should print their addition & average.

54

Precedence Rules, cont

e following list contains the precedence rules for some C++
erators:
unary
binary arithmetic
binary arithmetic
Boolean operators
Boolean operators
Boolean operator
Boolean operator
assignment

(), [], ., ->, (postfix)++, (postfix)-+(unary), -(unary), ++(prefix), --(prefix), !, sizeof
*, /, %
+, <, >, <=, >=
==, !=
&&
||
=,+=,-=,*=,/=,%=

example, consider (x+1) > 2 || (x+1) < -3,
s is equivalent to ((x+1) > 2) || ((x+1) < -3) because < and
have higher precedence than ||.

55

Boolean Expressions
The C++ data type bool is new. it was added to C++ recently. C++
used the integers 1 and 0 for true and false. in fact, anything other
than 0 was considered true. Although you can use integer values
instead of values of type bool, you shouldn’t. The capability is left
there for backward compatibility only. Use bool types instead.
Example:
if (1)
cout<<“True”<<endl;
else
cout<<“False”<<endl;
The point is that you should be aware of this feature of C++. Not
that you should use it in your programs.

56

Multi-way if-else statements
An if-else statement is a two-way branch. it allows a program to
choose one of two possible actions. Sometimes, you will want to have
a three- or four-way branch so that your program can choose
between more than two alternative actions.
You can do this by nesting if-else statements. For example, suppose
we want to write a game-playing program in which the user must
guess the value of some number.
cout<<“Guess the number: “;
cin>>guess;
if (guess >number)
cout<<“No, too high”;
else if (guess==number)
cout<<“Correct!”<<endl;
else
cout<<“No, too low”<<endl;


57

Multi-way Branches, cont

The indenting used in the example on the previous slide was different
from what we have been using. if we followed our indenting rules, we
would produce something like the following:
if (guess>number)
cout<“No, too high”<<endl;
else
if (guess == number)
cout<<“Correct”<<endl;
else
cout<<“No, too low”<<endl;

This is one of the rare cases where you should break the indenting
rules and use the layout on the previous page rather than the one
above. This is because the format on the previous page is clearer
and easier to understand than this one. Also, this way you save space.

58

Switch-statement
You used if-else statements to construct multi-way branches. The
switch-statement is another kind of C++ statement that also implements multi-way branches.
When a switch-statement is executed one of a number of different
branches is executed. The choice of which branch is executed is
determined by a controlling expression given in the parentheses
after the keyword switch.
The controlling expression must always evaluate to either a bool,
char, int or an enum type. When the switch-statement is executed,
this controlling expression is evaluated and the computer looks at
the constant values given after the various occurrences of the
identifiers case. if it finds a constant that equals the value of the
controlling expression, it executes the code for that case.

59

Switch-statement, cont
Let’s look at an example involving a switch-statement:
char grade;
cout<<“Enter your grade: “;
cin>>grade;
switch (grade)
{
case ‘A’:
cout<<“Excellent.”<<endl;
break;
case ‘B’:
cout<<“Very good.”<<endl;
break;
case ‘C’:
cout<<“Passing”<,endl;
break;
case ‘D’:
case ‘E’:
cout<<“Too bad, go study”<<endl;
break;
default:
cout<<“This is not a possible grade”<<endl;
}

60

Switch-statement, cont
Notice that the constant is followed by a colon. Also note that you
cannot have two occurrences of case with the same constant value
after them since that would be an ambiguous instruction.
A break-statement consists of the keyword break followed by a
semicolon. When the computer executes the statements after a
case label, it continues until it reaches a break-statement and this is
when the switch-statement ends. if you omit the break-statement,
then after executing the code for one case, it goes on to execute
the code for the following case.
The grades ‘D’ and ‘F’ cause the same branch to be taken. if the
value of grade is anything other than ‘A’, ‘B’, ‘C’, ‘D’, ‘E’, ‘F’ then the
cout-statement after the identifier default is executed.

61

++ and – Operators Revisited

You use the increment operator (++) to increase the value of a variable
By one. For example:
int number=2;
int value_produced=2*(number++);
cout<<value_produced<<endl;
cout<<number<<endl;

The output will be 4 andf then 3.

The new value is assigned AFTER the increment operation. You can
use ++ before the variable name like:
int number= 2;

int value_produced=2*(++number);
cout<<value_produced<<endl;
cout<<++number<<endl;
And this will output 6 and the 4. The increment operation is done BEFORE
the variable is used.

62

For-statement
The while-statement and the do-while statement are all the loop
mechanisms you need. in fact, the while-statement alone is enough.
But there is one kind of loop that is so common that C++ includes a
special statement for this kind of loop.
in performing numeric calculations, it is common to do a calculation
with the number one, then with the number two and so forth until
some last value is reached.
For example to add one through ten you
want the computer to perform the following statement ten times
with the value of n equal to 1 the first time and with n increased by
one each subsequent time.
sum=sum + n

63

For-statement
The following is one way to accomplish this with a while statement:
sum=0;
n=1;
while (n<=10)
{
sum=sum + n;
n++;
}

Although a while-loop is OK here, this kind of situation is just what
the for-loop was designed for. The following for-loop will neatly
accomplish the same thing:
sum=0;
for ( n=1; n <= 10; n++)
sum=sum + n;

64

For-statement
An example involving a for-loop:

initialization

main()
{
int sum=0;
for ( int n=1; n <= 10; n++)
{
sum = sum + n;
}

repeat the loop
as long as this is true
done after each
loop body iteration

cout<<“The sum of the numbers 1 to 10 is : “<<sum<<endl;
return 0;
}

65

break-statement
You have already used the break-statement as a way of ending a
switch-statement. This same break-statement can be used to exit a
loop.
Sometimes you want to exit a loop before it ends in the normal way.
For example, the loop might contain a check for improper input and if
some improper input is encountered then you may want to end the
loop. To input a list of negative numbers and exit the loop if positive
numbers are input:
int count=0, sum=0, number=0;
while (++count <= 10)
//ten loop iterations
{
cin>>number;
//input number
if (number >= 0)
break;
//exit loop
sum = sum + number;
}

66

Continue statement
We saw on the previous slide how to use the break-statement to
exit from a loop or from a switch-statement case. There is another
control statement that you can use in your programs: the
continue statement.
The continue statement causes the current iteration of a loop to
stop and the next iteration, if there is one, to begin. For example
consider the following code fragment:
while (true)
{
cin>>letter;
if ( letter== ‘ ‘ ) continue;
…
}

67

Which Kind of Loop to Use

We have seen three kinds of loops in C++ so far. That’s all there is
on loops in C++. As we have shown, you can do everything with just
the while-loop. The do-while loop is just an extension of the while
oop. And you can also use a while-loop instead of a for-loop after
ust a few changes.

But in general: if the loop involves a numeric calculation using a variable
That is changed by equal amounts each time through the loop, use a
For-loop. it is the clearest and easiest loop to use for numeric calculations.

n most other cases, you should use a while-loop or a do-while loop.
t is quite easy to decide which of these to use. if you want the
Loop body executed at least once use a do-while loop, otherwise use
A while-loop.

68

Exercises
15. Write a multi-way if-else statement that classifies the value of
an int variable n into one of the following categories and writes an
appropriate message:
n < 0 or 0 <= n <= 100 or n > 100
16. What is the output of the following fragment:
int count=3;
while (count-- > 0)
cout<<count<<“ “;

int count=3;
while (--count > 0)
cout<<count<<“ “;

69

Exercises, cont
int n=1;
do
cout<< n << “ “;
while (n++ <= 3);

int n=1;
do
cout<< n << “ “;
while (++n <= 3);

for (int count=1; count < 5; count++)
cout<< (2 * count) <<“ “<;

70

Exercises, cont
21. For each of the following situations, tell which type of loop would
Be better:
a. summing a series, such as ½ + 1/3 + ¼ + … +1/10
b. inputting the list of exam marks for one student
22. Rewrite the following code as a for-loop:
int i=1;
while ( i <= 10)
{
if (i < 5 && i !=2)
cout<<‘X’;
i++;
}

71

Exercises, cont
int i=1;
while ( i <= 10)
{
cout<<‘X’;
i = i + 3;
}
long m=100;
do
{
cout<< ‘X’;
m = m + 100;
}while ( m <= 1000);

72

Arrays
An array is a collection of variables all of the same data type that
are referred to by a common name. A specific element in an array is
accessed by an index.
in C++ the array elements are stored in contiguous memory locations.
The lowest address refers to the first element and the highest
address refers to the last element.
For example, to store a list of exam marks for students we can use
an array as in:
int mark[5];
This array is of type integer and it can hold 5 variables of type
integer. ‘mark’ is the name of this array.

73

Arrays, cont

The array declaration (similar to variable declaration) on the previous
slide is like the following declarations:
int mark1, mark2, …, mark5;

You can see that the array notation is clearer and more elegant.

The array int mark[5]; declares an array of type integer that
can store 5 variables all of type integer.

Array elements are numbered from 0. That is, the index of the first
Element in the array is 0 and the index of the last element is one
less than the size of the array. ( in this example, first element has
index 0 and last element has index 4)

74

Array initialization
You can initialize arrays in this way:
int mark[5] = { 87, 67, 90, 89, 100};
The size of this array is 5. The size of the array need not be
declared if it can be inferred from the values in the initialization:
int mark[ ] = { 87, 67, 90, 89, 100};
To access array elements we use the array name plus the index of
the required element. For example to output the second element
of this array:
cout<< mark[1]<<endl;
and the last element:
cout<< mark[4];

75

Arrays, cont
main()
{
int number[5];
for (int i=0; i<5; i++)
{
number[i]=i;
//initialize the array
cout<<i;
cout<<"t"<<(number[i] * number[i])<<endl;
}
return 0;
}

76

Arrays, cont
Let’s now look at the previous program more closely:
•

because the array has five elements (its size is 5) we write a
for-loop that iterates five times.

•

During each iteration, we initialize the next element of the array
and output that element on the screen. Then, we also output
the result of squaring each array element on the screen.

•

The escape character ‘t’ is used to create a tab space between
the array element and its square value.

it is very common to use for-loops to step through array elements
one by one.

77

Arrays in Memory
Array indexed variables are stored in memory in the same way as
ordinary variables are stored. But with arrays, the locations of the
Array indexed variables are always placed next to one another in the
computer’s memory.
For example consider the following array declaration:
int mark[5];
When you declare this array, the computer reserves enough memory
To hold 5 variables of type integer and the computer always places
These variables one after the other in the memory. The computer
Then remembers the address of the indexed variable mark[0], but it
Does not remember the address of any other indexed variable.
When your program needs the address of some other indexed
variable the computer calculates the address of this other variable
from the address of mark[0].

78

Arrays, cont
The most common programming error made when using arrays is
attempting to reference a non-existent array index. For example
consider the following array declaration:
int mark[5];
For this array, every index must evaluate to one of the integers
between 0 and 4. if you write:
cout<<mark[i]<endl;
Then i must evaluate to one of: 0, 1, 2, 3, 4. if it evaluates to
anything else it is an error. This is an out of range error.
Be especially careful when using for-loops to manipulate arrays.

79

Exercises
26. Describe the difference in meaning of int x[5]; and the meaning
Of x[4];
27. in the array declaration
double score[6];
what is the
a. the array name
b. the base type
c. the declared size of the array
d. the range of indexes that are OK for accessing the elements
e. one of the indexed variables (or elements) of this array

80

Exercises, cont
28. identify any errors in the following array declarations.
a.
b.
c.
d.

int x[4] = { 8, 7, 6, 4, 3};
int x[] = { 8, 7, 6, 4};
const int SiZE = 4;
int x[SiZE];
const int SiZE = 4;
int x[SiZE – 4];

29. What is the output of the following code fragment:
char symbol[3]= { ‘a’, ‘b’, ‘c’};
for (int index =0; index < 3; index++)
cout<<symbol[index];

81

Exercises, cont
double a[3] = { 1.1, 2.2, 3.3};
cout<< a[0]<<“ “<<a[1]<<“ “<<a[2]<<endl;
a[1]=a[2];
cout<< a[0]<<“ “<<a[1]<<“ “<<a[2]<<endl;
31. What is wrong with the following piece of code:
int array1[10];
for (int index=1; index <= 10; index++)
array1[index]=3*index;
32. Write a full complete C++ program to fill an array with 20
values of type integer from the keyboard. The program should also
Output the square and square root of each array element next to it
Like a table.

82

Structures
So far, we have only seen basic data types which had single data
items. Now we will look at a data type that is user defined and is a
composite type. You can define your own composite data types using
structures.
For example, if you want to represent a point in the two-dimensional
plane, you would need two values: one for the x-axis and one for the
y-axis ( the point coordinates) You can represent a point as a data
type whose type is a structure consisting of two values of type int.
struct point
{
int x;
int y;
};

83

Structures, cont
The structure ‘point’ which we defined on the previous slide, is a new
user defined data type. You can declare variables of this type in
your programs which include its definition. To declare a variable
of this new type, you follow the same method as we did for basic
data types:
point firstPoint;
The variables inside the structure are called member variables and
their values the structure’s member values.
Member variables are specified by giving the name of the structure
variable followed by a dot and then the member name. For example
to initialize the variable ‘point’ from last slide:
firstPoint.x=0;
firstPoint.y=0;

84

Structures, cont

But it is more common to initialize structures as in

firstPoint = {0, 0};
Do not forget the semicolon at the end of the definition of a structure
type and at the end of initialization.

Also, like other basic data types, you can assign one structure variable
To another variable of the same type as in
point firstPoint, secondPoint;
firstPoint={1,2};
secondPoint=firstPoint;
But you cannot compare structures with each other:
if (firstPoint==secondPoint)
if ((firstPoint.x==secondPoint.x) &&
(firstPoint.y==secondPoint.y))

//illegal
//OK

85

Structures, cont
Let’s look at an example program in which we define and use a structure:
#include <math.h>
struct point
{
int x;
int y;
};
main()
{
point firstPoint={4,9};
point secondPoint={5,10};
double distance=0.0;
distance = sqrt(((secondPoint.x – firstPoint.x)*
(secondPoint.x – firstPoint.x)) +
((secondPoint.y – firstPoint.y)*
(secondPoint.x – firstPoint.x)))
cout<<“the distance between points (4,9) and (5,10) is “<<distance<<endl;
return 0;
}

86

Strings

C++ can manipulate text strings in two ways: using cstring values used
in C language and with the new string type that was recently added
to the language. We will cover both methods in these slides.

A cstring variable is exactly the same thing as an array of characters.
For example, the following array of characters is capable of storing
a cstring value with 9 or fewer characters:
char name[10];

This is because a cstring variable is used in a differernt way than
an ordinary array of characters. A cstring variable places the special
symbol ‘0’ in the array immediately after the last character of the
cstring.


87

Strings, cont
For example, consider the following cstring variable:
char name[10] = “MR Nice”;
name[0]
M

r

N

i

c

name[9]
e

0

?

?

The character ‘0’ is used to mark the end of the cstring. Since the
character ‘0’ always occupies one element of the array, the length
of the longest cstring that the array can hold is one less than the
size of the array.
The character ‘0’ is called the null character. You can do input and
output with cstring variables as you do with other types of variables.


88

Strings, cont
You cannot use a cstring variable in an assignment statement using =.
Also, if you use == to test cstrings for equality, you will not get the
result you expect. The reason is that cstrings and cstring variables
are arrays rather than simple variables and values.
So you CANNOT do the following:
char name[10];
name=“Mr Nice”;
This is illegal in the homeland of C++!. You can only do this when you
declare the cstring variable as in:
char name[10]=“Mr Nice”;
Technically, this is an initialization and not an assignment and is legal.

89

Strings, cont

There are a number of ways to assign a value to a cstring variable.
The easiest way is to use the predefined function strcpy as in:

strcpy(name, “Mr Nice”);
This will assign (assignment) the value “Mr Nice” to character array
name.

Also, you CANNOT use the operator == in an expression to test if two
cstrings are equal. You can use the function strcmp as in:
char name1[]=“Mr A”, name2[]=“Mr B”;
if (strcmp(name1, name2)
cout<<“The two names are NOT the same”<<endl;
else
cout<<“The two names are the same”<<endl;

90

Strings, cont

Note that the function strcmp works differently than you might
expect. if the function returns a zero it means that the two
cstrings are the same (equal).

The functions strcpy and strcmp are defined in the library file
string.h so you must include this library in your C++ programs to be
able to use the functions.

Another useful function in this library is called strlen which returns
the length of the specified cstring. (‘0’ is not counted) For example:
int length=0;
char name[]=“Software Engineering”;
length=strlen(name);
cout<<length<<endl; //will output ?

91

Strings Input and Output

As we have already seen, cstring output is easy; we just use the
insertion operator << to do output.

Also you can use the input operator >> to fill a cstring variable, but
there is one thing to be aware of. All spaces are skipped when cstrigs
are read this way. For eg.
char a_cstring[20];
cout<<“Enter some input:n”;
cin>>a_cstring;
cout<<a_string<<endl;

The output:
Enter some input:
Mr Nice
Mr

92

Strings input and Output, cont
So there is a problem with cstring input when input contains spaces
or tabs. The solution to this problem is to use the predefined
function getline which is also defined in the string.h library.
Let’s see an example:
char a_cstring[30];
cout<<“Enter some text:n”;
cin.getline(a_cstring, 30);
cout<<a_cstring<<endl;
Here, the inputted text or string is copied into the cstring variable
a_cstring. The number 30 specifies the number of characters to
be copied into the variable a_cstring. (we will discuss functions
after finishing this topic)

93

Exercises
33. Consider the following two statements and whether they are
true or false:
a. the types of an array elements must all be the same?
b. the types of a structure’s members must all be the same?
34. Consider the following code:
struct student
{
char name[20];
int year;
bool male;
};
student software_student;

What is the type of

a. student.male?
b. student.name?
c. software_student?


94

Exercises, cont
35. What is the output of the following code:(if included in a
complete program)
struct student
{
char name[20];
int year;
};
student software_students[30];
for(int i=0; i<30; i++)
{
cout<<“Enter student’s name:”
cin.getline(software_student[i].name, 20);
cout<<“Enter student’s year:”;
cin>>software_students[i].year;
cin.ignore(1, ‘n’); //don’t worry about this now
}
cout<<“Software students are the following:”;
for(int j=0; j<30; j++)
cout<<software_students[i].name<<“ “<<
software_students[i].year<<endl;

95

Exercises, cont
36. Define a structure called student with the following member
variables:
•
•
•
•

Student’s name
Male/Female
Date of Birth
Students Exam Marks

Note:
1. You should define another structure which can represent a
calendar date.
2. You should also define a structure to represent the marks that
each student has obtained in each subject.
3. Number of subjects is pre-determined.

96

Exercises, cont
37. Write a C++ program that can maintain information about a
personal bookshelf. The program asks for information about a new
book such as the author, title, ISBN no., price, year published. Use a
structure to hold book information.
38. Find as many errors as you can find in the following piece of C++
code:
struct employee
{
char name[];
char address[30];
bool married;
double salary;
}
employee college_employees[100];
for (int i=0; i<=100; i++)
college_employees[i].salary *=1.2;

97

Exercises, cont
39. Write a program in which the user can input their full name (
consisting of exactly two words separated by a space). Store the
complete name, including the space, into a single cstring variable.
Then separate the two words and store them in two separate cstring
variables. Test your program.
40. Based on the previous program, write another program in which
the user enters their name such as
XXX YYYYYY
And then the program rearranges the first and last names into
YYYYYY, XXX
41. Write a program that accepts a word from the user and outputs
the number of vowels in that word. (Vowels include: A, E, I, O and U)


98

Functions and Procedural Abstraction

A natural way to solve large problems is to break them down into a
series of smaller sub-problems, which can be solved more-or-less
independently and then combined to arrive at a complete solution.

In programming too, you can follow a similar approach and divide large
programs into smaller sub-programs; in C++ sub-programs are called
functions.

Most programs consist of 3 main sections: input, some calculations
and output. We can perform each of these sections separately and
combine the results to produce the final complete program.

In larger programs, it’s almost impossible or very difficult to do
anything without dividing the program using functions. This follows
the old Roman philosophy of divide-and-conquer.

99

Functions, cont
We have already seen functions such as sqrt(…) to get the square
root of a number. Or the strcpy(s1, s2) which copies one string
to another.
These are pre-defined functions that we can use in our programs.
Somebody else has defined them; we just use them and we even don’t
need to know how the are defined as long as we know how to use
them.
The function sqrt(…) is defined in a file that we can access via the
C++ library ‘math.h’. And the function strcpy(s1, s2) is defined
in a file which we can access via the library ‘string.h’.
You can have user-defined functions too. You can define your own
functions to do specific tasks.

100

Functions, cont

In the next few slides we will try to write our own functions. At first
we will put these functions in the same file as “main”. Later we will
see how to put them in separate files. Example:

int area(int length, int width);

//function declaration

main()
{
int this_length, this_width, rectangle_area;
cout<<“Enter the length followed by width:”;
cin>>this_length>>this_width;
rectangle_area=area(this_length, this_width); //function call
cout<<“The rectangle area is “<<rectangle_area”<<andl;
return 0;
}
int area(int length, int width)
//start of function definition
{
int number;
number= length * width;
return number;
//function returning a value
}

101

Functions, cont
We will now look at this program closely to see how functions work:
• The structure of a function is similar to the structure of “main”
with its own list of variable declarations and statements
•

A function may have a list of zero or more parameters inside its
brackets, each of which has a separate type.

•

A function must be declared before it can be used or called.
Functions are declared just before the ‘main’ function begins.

•

Function declarations are a bit like variable declarations; they
specify which type the function will return.

•

You can define as many functions as you require provided you
declare them first.

102

Functions, cont

The function ‘area(…,…)’ returns a value of type int. And it takes
two parameters. A parameter is variable; during a function call this
parameter is replaced with a value.

In the this function, we have two parameters, both of type int.
When we call the function area(…,…) we pass two variables,
this-length and this-width, to the function. The function
area(…,…)then does some action on these variables and at the
end, returns some value of type int.

The parameters in the above function are called value parameters.
When the function is called in the main function, it is passed the
current values of the variables this_length and this_width. The
function then stores these values in its own local variables and uses
its own local copies in its subsequent computation.

103

Exercises
42. What is the output of the following program?
bool is_even(int number); //function declaration
main()
{
int i=0;
cout<<“enter a number: “;
cin>>i;
if (is_even(i))
cout<<i<<“ is even”<<endl;
else
cout<<i<<“ is odd”<<endl;
return 0;
}
bool is_even(int num)
{
if (num % 2 == 0)
return true;
else
return false;
}

104

Exercises, cont
43. Write a function that takes three parameters of type int. The
function returns the sum of its three parameters. Test the function
in a complete C++ program that asks the user for 3 numbers to be
added.
44. What does the following function do? Embed it in a full program
and test it.
int factorial(int n)
{
int product = 1;
while ( n > 0)
//n must be nonnegative
{
product = n * product;
n--;
}
return product;
}

105

Exercises, cont
45. Consider the declarations/prototypes of the following predefined mathematical functions:
double
double
double
double

sqrt(double x);
//returns square root of x
pow(double x,double y); //returns x to the power of y
ceil(double x);
//returns ceiling of x
floor(double x);
//returns floor of x

What would be the value of the 4 local variables if the following
function was called with num1=2.0 and num2=2:
int myFunction(double num1, double num2)
{
double localVar1, localVar2, localVar3, localVar4;
localVar1 = sqrt(num1);
localVar2 = pow(num2, 3.0);
localVar3=ceil(localVar1);
localVar4=floor(localVar1);
return 0;
}

106

Type Casting
Remember that 9/2 is integer division, and evaluates to 4 , not 4.5.
If you want division to produce an answer of type double, then at
least of the two numbers must be of type double. Ex, 9/2.0 returns
4.5.
We can do this because we had constants and we added a decimal
point and a zero to one or both numbers. BUT if both the operands
in the division are variables, not constants, then we would have a
problem.
In C++ you can tell the computer to convert a value of one type to a
value of another type:
double(9)/2
produces 4.5 because the type double can also be used as a predefined function. Another ex, double(2) evalutaes to 2.0.
This is called type casting.

107

The Black Box
A person who uses a program should not need to know the details of
How the program is coded. That person should know how to use the
Program but not how the program works.
A function is like a small program and should be viewed in a similar
way. A programmer who who uses a function needs to know how to
use the function but not how the function does its job. This is what
is meant when viewing a function as a black box.
Writing functions so that they can be used as a black boxes is
sometimes called information hiding or procedural abstraction.
The word procedure is a general name for functions. The word
abstraction is intended to convey the idea that when you use a
function as a black box, you are abstracting away the details of
the code in the function body.

108

The Black Box, cont

The term black box, information hiding and procedural abstraction
all refer to the same principle. They all mean the same thing.

The basic idea is that the programmer who uses a function should not
need to look at the body of the function definition to see how the
function works.

The function prototype/declaration and the accompanying comment
should be all the programmer needs to know to use the function.

It’s very important to comment your functions. The comments should
describe what the function does, not how. They should also mention
any conditions that are required of the parameters to the function
and describe the value that is returned by the function. Consider the
Predefined function sqrt, we can use it without knowing how it works.

109

Local Variables

As we have already seen in some of the functions that we have
defined, you can have variables declared inside those functions.

These variables exist only when you call the function to which they
belong. Variables declared inside functions are called local variables.

The scope of a local variable is the function inside which that variable
is declared. It doesn’t exist outside that function.

If you have a local variable in a function, you can have
another variable with the same name that is declared in the main
function or in another function and these will be different variables.

Remember that main is also a function; but a special one. Every C++
program must have the main function.

110

Global Constants and Global Variables

In general, constants are declared outside any functions, even outside
the main function. This is good programming as it is usually the case
that more than one function uses the same constant.

Constants are therefore usually declared as a group and just after
any #include directives. Hence the name global constant.

Also, you can declare variables outside any function definitions.
These are called global variables. The scope of global variables is
the entire program, unlike local variables whose scope is limited to
a particular function.

However, there is seldom any need to use global variables. Also,
global variables make a program harder to understand and maintain.
So we will not use global variables unless in exceptional cases.

111

Void Functions

The functions that we have seen so far all returned a single value. In
C++ a function must either return a single value or return no values at
all. A function that returns no value is called a void function. Ex.

void myFunction(int num);
{
num++;
cout<<“ one plus your number is “<<num<<endl;
}

As you can see, this function returns no values; it has no return
statements. You call void functions like other C++ statements as in:
main()
{
int x=0;
myFunction(x);
retrun 0;
}

//function call

112

Call-by-Reference Parameters
Will the function in the following program swap values of x1 and x2?
main()
{
int x1=5, x2=10;
swap(x1, x2);
cout<<“now x1 is “<<x1<<“ and x2 is “<<x2<<endl;
return 0;
}
void swap(int num1, int num2)
{
int temp=num1;
num1=num2;
num2=temp;
}

No, it will not. Because here, x1 and x2 have been passed to swap by
value. Copies of x1 and x2 are made and passed to swap and any
changes to their values,inside the function, occur on the copies of
the two variables.

113

Call-by-Reference Parameters, cont
The parameters x1 and x2 are call-by-value parameters. The value
of the parameters is passed to the function not the variables
themselves.
To ensure that the actual variables are passed to the function C++
supports call-by-reference parameters. This way, the address or
the actual variables are passed to the function. To correct the swap
function we need to use reference parameters as in:
void swap(int& num1, int& num2)
{
int temp=num1;
num1=num2;
num2=temp;
}

//call-by-reference parameters

Notice that you need to append the ampersand sign & to the name.

114

Exercises
void average(int& x, int& y, int&z);
main()
{
cout.setf(ios::fixed);
cout.setf(ios::showpoint);
cout.precision(2);
int num1=0, num2=0, num3=0;
cout<<“Enter 3 numbers:”;
cin>>num1>>num2>>num3;
cout<<“The average is “<<average(x, y, z)<<endl;
return 0;
}
void average(int& x, int& y, int& z)
{
return double(x + y + z))/3;
}

115

Exercises, cont
bool isInArray(int a[],int num);
main()
{
int x, a[]={2,3,4,5};
cout<<"enter a number:"<<endl;
cin>>x;
if (isInArray(a, x))
cout<<"yes"<<endl;
return 0;
}
bool isInArray(int a[], int num)
{
for (int i=0; i<4; i++)
if (num==a[i])
return true;
return false;
}

116

Exercises, cont
48. Write a function to find the smallest number in an array of type
int. Declare the array size to be 7 and fill the array from the
keyboard. The function should take the array as a parameter and
return the smallest number as the return value. Test the function
in a complete program.
49. Rewrite the above function as a void function and get the
function to change the value of a variable passed on to the function
as a parameter.
50. Write a program that takes 2 dates and then calculates the
number of days between those 2 dates. You can create a new data
structure as Date to represent calendar dates. Use a function that
takes two dates as parameters and calculates the number of days
between them.

117

Exercises, cont
51. From school you know that the standard quadratic equation
ax2 + bx + c = 0
has two solutions given by formula
-b

+ b2 – 4ac
2a

Write a function that reads a, b and c and then calculates the two
solutions. If the quantity under square root is negative it should
display an appropriate message. You may assume that the value for
a is nonzero. Test the function in complete program.


118

Exercises, cont
52. You have seen the pre-defined math.h function pow which takes
two double parameters and returns the power of first parameter
raised to the second parameter. Write your own pow function and
call it myPow. Test your program in a complete program.
53. Write a function that takes two int arrays as parameters and
if the two arrays are equal, ie have the same elements, it should
return true otherwise false. Test your program in a complete
program.
54. Write a function that takes two character array strings as
parameters and if the two strings are equal it should return
true otherwise false. Test your program in a complete program.


119

Sorting Arrays

One of the most common programming tasks is sorting a list of values
from highest to lowest or vice versa or a list of words into
alphabetical order.

There are many sorting algorithms; some are easy to understand but
not so efficient while some are efficient but hard to understand.
One of the easiest sorting algorithms is called selection sort.

The selection sort algorithm works as follows:
for( int index=0; index<ARRAY_SIZE; index++)
Place the indexth smallest element in a[index]

Where a is an array and array-size is the declared size of the array.
algorithms are usually expressed in pseudo-language.

120

Sorting Arrays, cont
The algorithm iterates through all the elements of the array one by
one and at each iteration it places the smallest number in the array
in the next suitable position.
Now we will implement this algorithm description in C++. We need
functions to do the following:
•
•
•

To find the smallest number in the array
To swap two values
To sort the array

We will now implement each of these functions separately and then
write a main function to test the functions.
(We have already implemented the swap function, see slide 112)

121


The sort function can be implemented as follows:

void sort(int array[])
{
int index_of_next_smallest = 0;
for(int index=0; index<ARRAY_SIZE-1; index++)
{
index_of_next_smallest=index_of_smallest(array, index);
swap_values(array[index], array[index_of_next_smallest]);
}
}

Notice that the last iteration is redundant (ARRAY_SIZE - 1
iterations)

We call another function to find the index of the next smallest value,
and then call yet another function to swap that value with the value
of the current position in the array.

122

Now we will implement the function which will find the index of the
next smallest element of the array:
int index_of_smallest((int array[], int start_index)
{
int min=a[start_index];
int index_of_min=start_index;
for (int index=start_index; index<ARRAY_SIZE; index++)
if (array[index] < min)
{
min=array[index];
index_of_min=index;
}
return index_of_min;

//return index of smallest number

}

123

Exercises, cont

55. Write a predicate function (whose return value is either true or
false) that takes an int array as a parameter and returns true if the
array is sorted in ascending order. Test your function in a program.

56. You can sort an int array by following the following procedure:

Start by going through the array, looking at adjacent pairs of values.
If the values of a pair are correctly ordered, do nothing; if they are
out of order, swap them. In either case move on to the next pair. The
pairs overlap so that the second element of the a pair becomes the
first of the next pair. Repeat this operation until you make a complete pass in which you do not make an exchange or swap of values.

This algorithm is called the bubble sort, because the values seem to
bubble up to their eventual positions.

124

I/O Streams

So far we have learnt how to input data from the keyboard and
output data to the screen. But for many real problem we need to be
able to input data from a file and out date into a file.

I/O from and into files can be done using C++ streams. Input stream
for data input from a file and output stream for output to a file.

You have already used some kinds of streams: cin (an input stream)
which is connected to the keyboard and cout (an output stream)
which is connected to the screen.

The main reason behind using I/O streams is because keyboard input
and screen output deal with temporary data. When the program ends
the data typed in at the keyboard and the output data to the screen
is lost. Files provide you with a way to store data permanently.

125

I/O Streams, cont

When your program takes input from a file it is said to be reading
From the file and when your program sends output to a file it is said
To be writing to the file.

When reading from a file, your program starts reading from the
beginning of the file and when writing to a file it starts writing to
beginning of the file.

A streams is a special kind of variable known as an object. As we said
Earlier there are both input and output streams. If you want a stream
To connect to a file, you must declare it as with variables.

The type for input file stream variables is ifstream and the type for
Output file stream variables is ofstream. Both of these types are
Defined in the library fstream.h.

126

I/O Streams, cont

Once you declare a stream variable of type ifstream or ofstream
you then must connect it to a file. This is called opening the file. Ex,

main()
{
ifstream input_file;
ofstream output_file;
input_file.open(“myInFile.txt”);
//opening the file
output_file.open(“myOutFile.txt”);
//opening the file
int num1, num2;
input_file>>number1>>number2;
//reading data
output_file<<num1<<“ “<<num2<<endl; //writing data
input_file.close();
output_file.close();
return 0;

//close file
//close file

}

127

I/O Streams, cont

In the previous example, one input stream and one output stream
were declared and then two files were opened, open for to read from
and one to write to.

Two numbers were read from the input file and these values were
then wrote to the output file using the output stream connected to
the output file.

Note that we only refer to the real name of a file once, when opening
the file. After a file is opened, the file is always referred to by
naming the stream that is connected to the file.

Also remember that every file should be closed when your program
is finished reading from a file or writing to a file. Forgetting to close
a file may result in a corrupted file.

128

I/O Streams, cont
Always check that a file was opened successfully. Trying to open a
file may fail for a number of reasons; for example, if there is no
file with such a name the call to open will fail.
You can use an input stream function called fail to test whether a
stream operation has failed. Ex,
input_file.open(“input.txt”);
if (inout_file.fail())
{
cout<<“Input file opening failed.n”;
exit(1);
//end the program
}

The exit statement causes your program to terminate immediately.
By convention, pass 1 for errors and 0 for success in. Exit(n) is
defined in library stdlib.h.

129

I/O Streams, cont

Let’s now look at a program that reads all the contents of a file, from
beginning to end of the file:

main()
{
int next, count=0;
double sum=0;
input_file.open(“myInFile.txt”);
//opening the file
while(input_file>>next) //also acts as a Boolean exp.
{
sum=sum + next;
count++;
}
cout<<“the average of numbers: “<<(sum/count)<<endl;
input_file.close();
//close file
return 0;
}

130

Character I/O
Every input stream, whether it’s an input file stream or the stream
cin has get as a member function. This function is used to read one
character of input. Unlike the extraction operator >>, get reads the
next character, no matter what that character is; it will even read
blanks (spaces), tabs, new-lines etc.
This function has one parameter which must be a variable of type
char. Ex,
char next_symbol;
cin.get(next_symbol);
This code will get the next character input from the keyboard and
store it in the variable next_symbol. Remember that the function
get can also be used with input file streams.

131

Character I/O, cont
The member function put is analogous to the member function get
except that it is used for output rather than input. Again as with
get, the member function put is a member function of every output
stream. Ex,
cout.put(next_symbol); //output it to screen
cout.put(‘b’);
//output ‘b’ to screen

This is some code to make a copy of one file (backup):

in.open(“input_file.txt");
out.open("output_file.txt");
char next;
in.get(next);
while(next != 'X') //make sure ‘X’ is in the file
{
out.put(next);
//write to output file
in.get(next);
// read next caharacter
}
// from input file

132

Character I/O, cont
The input file stream has a useful function which can be used to
determine when all of a file has been read and there is no more
input left to be read. This is the second technique we have seen for
determining end of files. This method is more suitable for text files
while the previous one is more suitable for files that consist of
numeric data. This function is called eof which stands for
end-of-file. Ex,
input_file.open(“input.txt”);
input_file.get(next);
while( ! input_file.eof())
{
cout.put(next);
input_file.get(next);
}

//or cout<<next;
//read next character

133

Character I/O Functions
There are a number of useful character I/O functions that can be
used to process text files. Among these functions are: (ctype.h)

- toupper(char_var) returns uppercase version of char_var
ex, toupper(‘a’)
returns ‘A’
- tolower(char_var) returns lowercase version of char_var
ex, tolower(‘H’)
returns ‘h’
- isspace(char_var) returns true if char_var is either a
space, tab or a new-line (‘n’), otherwise returns false
ex, isspace(‘ ‘) returns true
- isupper(char_var) returns true if char_var is uppercase letter,
ex, isupper(‘L’) retruns true
- islower(char_var) returns true if is char_var is a lowercase
letter, ex, islower(‘r’) retruns true
- isalpha(char_var) returns true if char_var is a letter of the
alphabet ex, isalpha(‘$’) returns false
- isdigit(char_var) returns true if char_var is one of the digits
0,1….9. Ex isdigit(‘5’) returns true;


134

Exercises
57. Write a function that takes as parameter the name of a file,
then it opens the file and outputs all the contents of the file onto
the screen. First create a text file and type some text in the file
and save it in the same directory. Test your function in a program.
58. Write a function that takes two file names as parameters and
copies the contents of the first file into the second file. Test your
Program in C++ program.
59. Write a function takes a file name as its only parameter. The
function will search the file of numbers of type int and write the
largest and smallest numbers to the screen. The file contains
nothing but numbers of type int separated by blanks or line breaks
or tabs. Test your function in a C++ program.

135

Exercises, cont

60. Write a program that reads text from one text file and writes
an edited version of the same text to another file. The edited
text is identical to the original version except that its text is all in
upper case.

61. Write a program that reads all the contents of a text file and
writes everything except numbers into another file. It filters
numbers from the file.

62. Write a function that takes three filenames as parameters. Two
input files and one output file. The input files consist of numbers of
type int only. The numbers in the two files are in sorted order from
the smallest to the largest. The output file will contain all the
numbers from the two input files in one longer list in sorted order
from smallest to largest. Test your function a C++ program.

136

Exercises, cont
63. This is a programming mini-project.
Write a program that defines a new structure called student
and asks the user to enter information on first year Software
Engineering students. The structure has name, year, grade as
structure member variables.
The program should write or save this information to an output file.
Then define a function to check whether a particular student name
is enrolled on this course. The function takes a student’s name as
Parameter and it then searches the file that contains student details
to see if that student is on the course. If he/she is then it should
print the students details on the screen.

137

Exercises, cont
64. Write a program to count the number of lines, the number of
words and the number of non-blank characters in a file. It
should then display this information on the screen.
A word is any sequence of characters between any two of following
characters: space, tab, new-line, comma, period. For this exercise
only consider spaces and new-lines.
65. Write a function that reads text from a file and writes each line
preceded by a line number starting from 1. Follow the line number
with a colon and a space for clarity. You may assume that the lines
are short enough to fit within a line on the screen. Test your
function in a C++ program.


138

Exercises, cont
66. Write a function to strip or remove comments (//) from a C++
source file. Do this program in stages. First write a function
with the prototype/declaration
void stripFile(ifstream &inFile, ofstream &outFile);

Which simply reads lines from the input stream inFile to a
character array and then output them to the output stream
outFile.
You need to store new-line characters explicitly as they
do not get stored in the character array automatically.

Then change your function to remove the comments from a file
whose name is input from the keyboard. The program should also
ask the user for the name of the output file. Test you function in a
C++ program.

139

Multidimensional Arrays
In C++, the elements of an array can be of any type. In particular,
the elements of an array can themselves be arrays. Arrays of arrays
are called multidimensional arrays.
The most common form of a multidimensional array is a twodimensional array which is similar to a rectangular structure divided
into rows and columns. This type of two-dimensional array is called a
matrix.
You can have arrays of 3 or more dimensions. They are less common.
Consider the two-dimensional array matrix:
int matrix[2][3]={{2,2,2},
{2,2,2}};

//two rows, three columns

This is an array (size 2) of two arrays (size 3).

140

Multidimensional Arrays, cont
We will now look at an example involving two-dimensional arrays; in
this example we will write a function to add to matrixes.
main()
{
int array1[4][2]={

0,1,
0,1,
0,1,
0,1};
int array2[4][2]={ 1,1,
1,1,
2,2,
2,2};
addMatrixes(array1, array2);
return 0;

}
cont…

141

The function takes two two-dimensional arrays as parameters. It
adds the two matrixes and puts the result into the first array. It
then prints the result matrix on the screen.
void addMatrixes(int a[][2], int b[][2])
{
for(int i=0; i<4; i++)
{
for(int j=0; j<2; j++)
a[i][j]=a[i][j]+ b[i][j];
}
// to display the result on the screen
for(i=0; i<4; i++)
{
for(j=0; j<2; j++)
cout<<array1[i][j]<<" ";
cout<<endl;
}
}

//adding

142


For multi-dimensional array parameters, all the dimension sizes
except the first must be given. This makes sense if you think of
a multi-dimensional array as an array of arrays. In this example we
have an array each element of which is an int array of size 4.
Remember that if you have an array parameter, you do not have to
specify the the array size in the square brackets.

Multi-dimensional arrays are mainly used to perform matrix
operations and numerical analysis calculations. The base type of a
multi-dimensional array can be any type; but for numerical calculations
the type is usually int or double.

In the example on the previous page, we saw how to add two matrixes.
You can also do other matrix operations like matrix multiplication,
matrix transformations using two-dimensional arrays.

143

Exercises
67. Write a function that has one parameter of type int array[][2]
The function multiplies its parameter by the unit matrix and prints
the result. Test your function in a C++ program.
68. Write a function that takes two parameters one of type
int a[2][5] and the other of type int b[5][2] and then multiplies
the two matrixes together and writes the result in a third matrix.
Test you function in C++ program.
69. Write a function that takes a parameter of type int a[5][5]
and changes the value of every element above the diagonal to 0 and
70. Write a function that takes a parameter of type int [4][4]
and exchanges the elements above and below the diagonal together.
Leave the diagonal values unchanged.

144

Pointers
A pointer is the memory address of a variable and can be stored in a
variable. But even though a pointer is a memory address and a
memory addresses are numbers, you cannot store a pointer in a
variable of type int or double. A variable to hold a pointer must be
declared to have a type. Ex.
double *p1, *p2, v1, v2;
p1 = &v1;
The variables p1 and p2 can hold pointers to variables of type double.
Also notice that you need to add an asterisk before the pointer
variable name.
Pointer variables can point to variables like v1 and v2 since they are
of type double. You can use the operator & to get the address of a
variable and then assign that address to a pointer variable.

145

Pointers, cont
Now we have two ways to refer to a variable: you can call it v1 or you
can call it “the variable pointed to by p1. In C++ you use *p1 to say
“the variable pointed to by p1”. This use of the asterisk operator is
called the dereferencing operator. To clarify things, consider this
piece of C++ code:
int v1, *p1;
v1=0;
p1=&v1;
*p=32;
cout<<v1<<“

“<<*p1<<endl;

What will this code produce? Because p1 is a pointer pointing to v1
then both *p1 and v1 refer to the same variable. So when you set *p1
to 32, you are also setting v1 to 32.

146

Pointers, cont
You can assign the value of one pointer to another pointer variable.
For example, if p1 is still pointing to v1, then the following will set p2
so that it also points to v1:
p2=p1;
and if we write
cout<<*p2;
this will also output 32.
Using pointers, you can use variables even if variables have no names
or identifiers. the operator new can be used to create variables that
have no identifiers as their names. These nameless variables are
referred to via pointers.

147

Pointers, cont
Consider the following piece of C++ code:
int *p;
p=new int;
cin>>*p;
*p=*p+1;
cout<<*p1;
the first statement creates a pointer of type int and the second one
creates an integer variable and sets p to point to this variable. This
nameless variable can be referred to as *p. Here we have an integer
variable but without a name; but we can use the pointer p to refer to
it.
Variables that are created using the new operator are called
dynamic variables. They are created and destroyed while the
program is running.

148

Pointers, cont

am to demonstrate pointers and dynamic variables:

*p1, *p2;
//two pointers of type int
new int;
// dynamic int variable
=32;
p1;
//assign p2 to p1
t<<“*p1: “ <<*p1<<“ “<<“*p2: ”<<*p2<<endl;
=53;
t<<“*p1: “ <<*p1<<“ “<<“*p2: ”<<*p2<<endl;
new int;
=88;
t<<“*p1: “ <<*p1<<“ “<<“*p2: ”<<*p2<<endl;
t<<“Hope you got the point of this example!!!”<<endl;
urn 0;

next slide for a pictorial explanation of this program.

149

Pointers, cont
1- int *p1, *p2;
p1 ?
p2 ?
2- p1=new int;
p1
p2 ?
?
3- *p1=32;
p1
p2 ?

32

(pictorial explanation of program)


4- p2=p1;
p1
p2

32

5- *p2=53;
p1
p2
53
6- p1=new int;
p1
?
p2
53
7- *p1=88;
p1
p2

88
53

150

Pointers, cont
There is a special area of memory reserved for dynamic variable.
This is called the heap. When you create a dynamic variable, the
variable consumes some of this memory.
If your program creates too many dynamic variables it will consume
all of the memory in the heap and any further calls to new will fail.
For this reason your program should always check to see if new
successfully created the dynamic variable. new returns a special
pointer called NULL when memory in heap has finished:
int *p;
p=new int;
if(p==NULL)
//NULL defined in stddef.h library
{
cout<<“Insufficient memory.n”;
exit(1);
}

151

Pointers, cont
If your program no longer needs a dynamic memory, the memory
consumed by that variable can be released or returned to the heap.
The operator delete destroys a dynamic variable and returns the
memory to the heap. Ex,
int *p;
p=new int;
//create a dynamic variable
some-statements
delete p;
//destroy dynamic variable/return memory

Note that delete destroys the dynamic variable, not the pointer
which points to that variable. When this happens you don’t know
what the pointer is pointing to. It could point to any part of
memory. These undefined pointers are called dangling pointers.
Another example of a dangling pointer is when two pointers point to
the same variable and if you delete one pointer the other pointer
will be a dangling pointer since you have returned the memory it
pointed to and don’t know what it points to now.

152

Dynamic Arrays

The arrays you have seen so far had a basic limitation and that was
that you must specify the array size when you write the program.
But sometimes you don’t know how big the array size will be.

If you specify the array size to be too big then if you do not make
use of all the array you are wasting memory. On the other hand,
if you specify an array’s size to be too small then your program will
not work in all situations.

Dynamic arrays avoid these problems. With dynamic arrays, you
do not have to specify the array size as you write the program; you
can do this when your program is running. You create a dynamic array
as you create a dynamic variable:
double *p;
p=new double[array-size]; //array-size is a variable

153

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