This document provides an overview of input and output operations, preprocessor directives, and debugging syntax errors in C++. It discusses including the iostream and string libraries for input/output and string processing. It covers input and output statements using cin and cout, constants, and increment/decrement operators. The document also reviews preprocessor directives like #include and #define, and manipulators for formatting output. It concludes with debugging syntax errors and understanding semantics.

1. CHAPTER THREE
MORE ON:
 INPUT AND OUTPUT,
 INCREMENT AND DECREMENT
OPERATORS,
 PREPROCESSOR DIRECTIVES,
 INPUT OUTPUT MANIPULATION,
 DEBUGGING (FIXING SYNTAX ERRORS)
LECTURER: Samson Mekbib

2. INPUT AND
OUTPUT
SUMMARY AND FEW MORE
POINTS
2

3. INTRODUCTION
 The keywords for input and output operations are stored in
the standard library called iostream
 Input = cin, output = cout
 To use the cout and cin commands in C++, you need to
include the following two lines:
#include <iostream>
Using namespace std;
 The first line which start with # is a preprocessor directive
 Lines that begin with # are preprocessed by the
preprocessor before the program is compiled
 The second line using namespace tells C++ to use the
standard names cout and cin
3

4. STRING DATA TYPE
 To use the string type in C++, we need to access its definition from
the header file string
 To process strings effectively, C++ provides the type string
 Include the following preprocessor directive:
#include <string>
4

5. CONSTANTS
 Some data must stay the same throughout a program
 In C++, you can use a named constant to instruct the program to mark those
memory locations in which data is fixed throughout program execution.
 Named constant: A memory location whose content is not allowed to change during
program execution
 The syntax to declare a named constant is:
Const dataType identifier;
Identifier = value;
 An equivalent form of the above syntax is:
Const dataType identifier = value;
 Examples:
const int No_of_students = 54;
const float Pay_Rate = 15.75
5

6. INPUT (READ) STATEMENT
 Syntax
cin >> variable >> variable …;
 cin is used with >> to gather input
 This is called an input (read) statement
 Using more than one variable in cin allows more than one
value to be read at a time
 Example:
cin >> feet >> inches;
 This will input tow values from the keyboard (specified by
the user) and places them in variables feet and inches
respectively.
6

7. OUTPUT
 Syntax:
cout << expression or manipulator << expression or manipulator …;
 Is call an output statement
 The stream operator is <<
 Text to be displayed must be typed in between double quotations
“””
 To print out values of identifiers like variables and constants we
write them without “”
7

8. MANIPULATOR
 A manipulator is used to format the output
 Example: endl causes insertion point to move to the beginning of
the next line.
 Instead of endl the new line character ‘n’ could be used
8

9. COMMONLY USED ESCAPE
SEQUENCE MANIPULATORS
9

10. SPECIAL STATEMENTS IN C++
 A C++ statement such as
num = num + 2;
means “evaluate whatever is in num, and 2 to it, and assign the
new value to the memory location num.”
 The expression on the right side will be evaluated first and then
that value will be assigned to the variable.
 Example:
num = 6;
num = num + 2;
 After running the second statement C++ will assign 8 to the
variable num.
10

11. SPECIAL STATEMENTS CONTD.
 Example: Suppose that num1, num2 and num3 are int variables and the
following statements are executed in sequence
1. num1 = 18;
2. num1 = num1 + 27;
3. num2 = num1;
4. num3 = num2/5;
5. num3 = num3 / 4; The output at the end of each step will be as follows:
 Before statement 1 no value was assigned to num1, num2, num3
 After statement 1 num1 equals 18 and no value assigned to num2 and
num3
 After statement 2 num2 equals 45 and no value assigned to num2 and
num3
 After statement 3 num1 equals 45, num2 equals 45 and no value assigned
to num3
 After statement 4 num1=45, num2=45, num3 = 9
 After statement 5 num1 = 45, num2 = 45, num3 = 2
11

12. INCREMENT AND DECREMENT
OPERATORS
 Often used by programmers and they are useful programming tools
 Suppose count is an int variable. The statement
count = count + 1;
Increments the value of count by 1.
 Such statements are frequently used to keep track of how many
times certain things have happened
 To simplify such statements C++ provides the increment operator,
++, which increases the value of a variable by 1, and the decrement
operator, --, which decreases the value of a variable by 1
 Syntax of pre-increment: ++variable
 Syntax of post-increment: variable++
 Syntax of pre-decrement: --variable
 Syntax of post-decrement: variable--
12

13. EXAMPLE - 1 ON PRE AND POST
- INCREMENT
 Consider the following statement:
x = 5;
y = ++x;
 The first statement assigns the value 5 to x. To evaluate the second
statement, which uses the pre-increment operator, first the value of x
is incremented to 6, and then this value 6 is assigned to y. After
second statement execute both x and y will have the value 6.
 Now consider the following statements:
x=5;
y = x++;
As before the 1st statement assigns 5 to x. In the 2nd statement since
post-increment is used, the value 5 before increment is assigned to y,
and x is incremented to 6. Hence after the second statement x = 6 and
y= 5.
13

14. EXAMPLE - 2 ON PRE AND POST
- INCREMENT
 Consider the following statement:
a = 5;
b = 2 + (++a);
 The first statement assigns the value 5 to a. To evaluate the second
statement, which uses the pre-increment operator, first the value of a
is incremented to 6, then 2 is added to it and the value 8 is assigned
to b. Therefore, after the second statement executes, a is 6 and b is
8.
 Now consider the following statements:
a = 5;
b = 2 + (a++);
After the second statement is executed the value of a is 6 while the
value of b is 7.
14

15. MORE PREPROCESSOR
DIRECTIVES
 In a C++ system, a preprocessor program executes automatically
before the compiler's translation phase begins
 Preprocessor directive statements will not end with a semicolon (;)
 So far we have seen the preprocessor directives #include
<iostream> and #include <string> that allows us to handle input out
operations and using the string variables respectively in C++
 Other preprocessor directive types are #include<filename>, which
are used to include saved C++ files with extension either .cpp or .h
 Another preprocessor directive type is #include<iomanip> that
allows some C++ output manipulation commands like setw().
 The manipulator set width is used for setting field output in C++
 Output manipulators we saw so far (n, t, ‘b’ etc.) do not need a
preprocessor directive. But to run the manipulator setw() we need to
write #include<iomanip> at the start of the program
15

16. SET WIDTH MANIPULATOR
 Syntax setw(num)
 setw() is library function in C++
 setw() is declared inside #include<iomanip>
 setw() will set field width
 Setw() sets the number of characters to be used as the field width for
the next insertion operation
16

17. 17

18. DEBUGGING: UNDERSTANDING
AND FIXING SYNTAX ERRORS
Compile a program
• Compiler will identify the syntax errors
• Specifies the line numbers where the error occur
Examples:
18

19. SYNTAX
 Syntax rules- indicate what is legal and what is not legal
 Error in syntax are found in compilation
 Errors and debugging is common in programming
 Examples
int x; //Line 1
Int y; // Line 2: error
float b // line 3: error
double z = w + x; // line 4: error, identifier w not defined
19

20. USE OF BLANKS
 In C++, you use one or more blanks to separate
numbers when data is input
 Blanks are used to separate reserved words and
identifiers from each other and from other symbols
 Blanks must never appear within a reserved word or
identifier
20

21. USE OF SEMICOLONS,
BRACKETS, AND
COMMAS
 All C++ statements end with a semicolon
 Semicolons are also called statement terminator
 Brackets like { indicate start of main function and a
closing bracket } indicates end of function main
 Commas are used to separate items in a list
21

22. SEMANTICS
 Semantics: set of rules that gives meaning in a language
• It is possible to remove all syntax errors in a program and still
not able to run it
• Even if it runs, it may still not do what we expect it to do
 Example: 2 + 3 * 5 and (2 + 3) * 5
are both syntactically correct expressions, but have different
meanings.
22

23. NAMING IDENTIFIERS
23

24. PROMPT LINES
24

25. DOCUMENTATION
25

26. FORM AND STYLE
26