Chapter 2

Structure of C++ program
Documentation section
Linking section
Definition section
Global declaration section
Function
main() functions
Chapter Two
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DMU ,INTRON_ TO C++ ECEG SEE IT IN
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 Documentation Section: comment parts, which are
ignored by compiler. The comments are used to describe
the functionality of each statement in the program, its
copyright, author, and date of compilation and purpose of
the program to the user.
Syntax: //This statement is a single line comment
/*This is multiline comment*/
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Link section:
 link the necessary files and libraries to current files
 Includes pre-processer directives as well as header
files
Syntax: #include<file or library name>
e.g. #include<iostream.h>
#include<iomap.h>
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Definition Section:
 It is possible to define symbolic constants.
 A symbolic constant is a constant value given to a
name which can't be changed in program
Syntax: #define identifier constant
e.g #define PI 3.14
 Global declaration Section: variables declared under
this section are available throughout the program.
syntax: data type variable
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main ( ) function:
 The execution of the program starts from main function.
 Every program must have only one main function.
 All other functions are called either directly or indirectly
from main
 It is independent from whether it is at the beginning, at the
end or by the middle of the code
 its content is always the first to be executed when a
program starts
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Syntax and Semantics
Syntax :
 consists of the rules for the correct use of the language.
 This involves the correct grammatical construction and
arrangement of the language, correct spelling.
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 Semantics:
deal with the meanings given to syntactically correct
constructs of the language.
is defined in terms of the program’s run-time behavior
A program could be syntactically correct yet
meaningless
Example
sum=0;
while (sum!=-1)
sum=sum+10;
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C++ Compilation Process A
 program written in C++ must be translated into a
machine language in order to be executed by a
CPU.
 The process of translating high-level language
into machine language
 The compilation process consists of the following
steps. edit source code -> compile -> link -
> execute (editor) (compiler) (linker)
(loader)

The parts of a simple C++ Program
 C++ program file should be saved with file name extension
“ .CPP ”
 #-is a signal to the preprocessor
 include - is a preprocessor instruction that directs the
compiler to include a copy of the file specified in the angle
brackets in the source code.
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Cont’d
 { } : signals the beginning of the main function body and the end
of the main function body
 ; statement ends with semicolon
 Cout: is an object used for printing data to the screen. followed
by the insertion operator also called output redirection operator
(<<)
Syntax: cout<<Object;
Cin:
 used for taking input from the keyboard. followed by the
input redirection operator (>>) also called extraction
operator.
 take value from the keyboard and store it in the memory
Syntax: cin>>Object
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return 0;
 makes the main() function to finish and return the code
that the instruction is followed by, in this case 0.
 most usual way to terminate a program that has not found
any errors during its execution.
Valid names—Identifiers
 Within a program names are used to represent variables,
constants and functions.
 When choosing valid identifiers for your variables,
constants and functions, the following rules will be applied.
1) an identifier contains a series of letters, numbers, or
underscore ( _ )
2) the first character must be a letter or underscore
3) no restriction on the length of an identifier
4) C++ keywords are reserved and can not be used as names
Cont’d
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Comments on C++ programs
 text which explains some aspect of a program.
 Ignored by the compiler
 Their purpose is only to allow the programmer to insert
notes or descriptions embedded within the source code
 C++ provides two types of comment
i. Single Line Comment:
Eg: cout<<var1; //this line prints the value of var1
ii. Multiple Line Comment:
Eg: /*this is a kind of comment where
Multiple lines can be enclosed in
one C++ program */
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Variables and Constants
Variable:
 is a reserved place in memory to store information in.
 is used for holding data values
 All variables have three important properties:
 Data Type: describes the property of the data and the size
of the reserved memory
 Name: used to refer to the value in the variable
 Value: assigning a new value to the variable
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Declaring Variables
 Variables can be created in a process known as declaration.
 Good variable names indicate the purpose of the variable or
they should be self descriptive.
 E.g. int myAge
Syntax: Data type Variable Name;
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Keywords
 having a predefined meaning in the language
 we cannot use them as variable names or any other
purpose other than their predefined usage.

Initializing Variables
 When declaring a variable, its value is by default
undetermined.
 When a variable is assigned a value at the time of
declaration, it is called variable initialization
The syntax is:
Data Type variable name = initial value;
 e.g. int a = 0;
or: int a;
a=0;
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Scope of Variables
There are two types of variable visibilities.
 Global variables:
 are variables that can be referred/ accessed anywhere
in the code, when any function, as long as it is declared
first.
 A variable declared before any function immediately
after the include statements are global variables.
Local Variables:
 the scope of the local variable is limited to the
code level or block within which they are declared.
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Characters
 Char in C++ are represented as any value inside
a single quote
 E.g.: ‘x’, ‘A’, ‘5’, ‘a’, etc.
Expressions and Statements
All C++ statements end with a semicolon
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Constants
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 A constant is any expression that has a fixed value.
 Like variables, constants are data storage locations in
the computer memory.
 But, constants, unlike variables their content cannot
be changed after the declaration.
 Constants must be initialized when they are created
by the program, and the programmer can’t assign a
new value to a constant later.
 C++ provides two types of constants: literal and
symbolic constant
e.g int studentperclass=15;
student=class*studentperclass

Operators
is a symbol that makes the
machine to take an action
C++ provides several
categories of operators
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Cont’d
Assignment operator
Arithmetic operator
Relational operator
Logical operator
Increment/decrement
operator
The size of operator
Explicit type casting 11/2/2019
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Assignment operator (=)
Syntax: Operand1=Operand2;
 Compound assignment operators: is the
combination of the assignment operator with
other operators like arithmetic and bit wise
operators.
Example:
(+=, -=, *=, /=, %=, >>=, <<=, &=, ^=)
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Arithmetic operators (+, -, *, /, %)
 Except for remainder or modulo (%), all other arithmetic
operators can accept a mix of integers and real operands
 Integer division always results in an integer outcome.
E.g.:
9/2 gives 4 not 4.5
-9/2 gives -4 not -4.5
 Division of integer by integer will not round off to the next
integer
E.g.:
int cost = 100;
int volume = 80;
double unitPrice = cost/ (double) volume;
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Cont’d
The modulo(%) is an operator that gives the remainder
of a division of two integer values
Relational operator (==, !=, > , <, >=, <=)
Is a comparison of two expressions
The result of a relational operator is a Boolean value
that can only be true or false
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Logical Operators (!, &&, ||)
 Logical negation (!)
is a unary operator
 negates the logical value of its
operand.
If its operand is non zero, it
produces 0, and if it is 0 it
produce 1.
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Cont’d
Logical AND (&&)
 produces 0 if one or both of its operands
evaluate to 0 otherwise it produces 1.
Logical OR (||)
 produces 0 if both of its operands
evaluate to 0 otherwise, it produces
1.
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Increment/Decrement Operators: (++)
and (--)
The auto increment (++) provide a
convenient way of adding 1 from a
numeric variable.
 auto decrement (--) operators
provide a convenient way of
subtracting 1 from a numeric
variable.
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Prefix and Postfix:
prefix :
• is written before the variable.
• is evaluated before the assignment.
 postfix :
• appears after the variable name.
• is evaluated after the assignment.
• Prefix and postfix operators can not be used
at once on a single variable.
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The size of() Operator
used for calculating the size of any
data item or type.
It takes a single operands
The outcome is totally machine
dependent.
E.g.:
a = size of(char)
b = size of(int)
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Explicit type casting operators
 allows you to convert a datum of a
given type to another data type.
E.g.
int i;
float f = 3.14;
i = (int)f;  equivalent to i = int(f);
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Operator Precedence
Operators in higher levels take
precedence over operators in
lower levels.
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Precedence Table:
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cont’d
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Example
 a = = b + c * d
 a = = (b + c) * d

Debugging
 Correcting programming errors
 Detecting ,checking abnormalities
 Also ,we said step by step procedure to find out
errors and removing it
Programming errors
-three types of errors
 Syntax error
 Runtime error
 Logical error
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Syntax error
This error occurs due to following reason.
 Not following the grammatical rules used in
declaration of identifier.
 Not declaring an identifier used in program.
 Not terminating statement by semicolon
 Not providing equal number of opening and
closing braces etc.
These errors can be rectified by the user as it is
displayed while compiling the program.
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Runtime error
This error occurs while running a program by displaying
the message listed below.
 Division by 0.
 Overflow,
 E.g. ,memory issue
 Harmful or malicious applications like computer viruses or
Hadware
 when a program calls too many methods or nested
processes
 Underflow
 is a condition in a computer program where the result of a
calculation is a number of smaller
 occur when the true result of a floating point operation is
smaller in magnitude (that is, closer to zero) than in the target
data type
 underflow also results in not having the result saved in the
memory of the application or device.
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Logical error
 This error won’t be displayed on the screen. However it will lead
to display wrong results.
Example: An infinite loop.
#include <iostream.h>
int main(){
int n = 1;
while( n > 0){
cout << n << endl;
n++; }
return 0;
}
 This error lead to abnormal termination of a program or infinite
loop.
 These errors solely depend on the logical thinking of the
programmer and are easy to detect if we follow the line of
execution and determine why the program takes that path of
execution.
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