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Looping means execution of a statement or block of statements repeatedly until the condition is true.

The loop evaluates the condition at the end of the looping structure and selects a statement for execution repeatedly. Therefore it is called a post-tested looping statement.

A ‘for’ loop is a repetition control structure, that allows you to efficiently write a loop that needs to execute a specific number of times.

Syntax:

The syntax of a ‘for’ loop in C++ is:

for (initialization; condition; increment/decrement)

{ 

statement(s);

}

The working of a ‘for’ loop:

1. The initialization step is executed first, and only once in the beginning. It is used to declare and initialize loop control variables.

2. Next, the condition is evaluated. If it is true, the body of the loop is executed. If it is false, the body of the loop does not execute and the flow of control jumps to the next statement just after the ‘for’ loop.

3. After the body of the ‘for’ loop executes, the flow of control jumps back up to the increment/ decrement statement and update any ‘loop’ control variables.

4. Then the condition is evaluated again. If it is true, the ‘ loop’ executes and the process repeats itself (body of ‘loop’, then increment step, and then again condition). After the condition becomes false, the ‘for’ loop terminates.

Example:

#include<iosteam>

int main()

{

//for loop execution

for(int a = 10; a <20; a = 1+ 1)

{

cout<<"value of a:"<<a<<end1;

}

return 0;

}

When the above code is compiled and executed, it produces following result:

value of a: 10

value of a: 11

value of a: 12

value of a: 13

value of a: 14

value of a: 15

A ‘while’ loop statement repeatedly executes a statement or sequence of statements written in the flower brackets as long as a given condition returns the value ‘true’.

Syntax: The syntax of a ‘while’ loop in C++ is: while(condition)

{

statement (s) ;

}

Here the condition may be any expression, and for true is any non zero value. The loop iterates while the condition is true. When the condition becomes false, program control passes to the line immediately following the loop. During the first attempt, when the condition is tested and the result is false, the loop body will be skipped and the first statement after the ‘while’ loop will be executed.

Example: #include<iostream>

int main ()

{

int a = 10;

while (a<15)

{

cout <<"value of a:"<<a<<end1;

a++;

}

return 0;

}

When the above code is executed, it produces the following result:

value of a: 10

value of a: 11

value of a: 12

value of a: 13

value of a: 14

The ‘go to’ statement transfers/jump control from one part of the program some other part. The ‘continue’ statement is used in loops and causes a program to skip the rest of the body of the loop.

The ‘break’ statement can be used to terminate a repeated structure (loops) such as ‘while’, do-while and for and multi-branching statements like ‘switch’.

The execution of a program can be stopped at any point with ‘exit ( )’.

Syntax of ‘do-while’ loop

do

{

statements;

}

while (condition);

Syntax of ‘while’ loop:

while(condition)

{

statement(s);

}

Syntax :

if(expression)

{

statements

}

else if(expression)

{

statements

}

else if(expression)

{

statements

}

Selection statements are used to execute certain block of statements by evaluating the conditions.

The different selection statements are

1. ‘if’ statement

2. ‘if-else’ statement

3. ‘if-else-if’ (nested) statement

4. ‘switch’ statement

If (condition)

{

statement 1;

....

statement n;

else

{

statement 1;

.....

statement n;

}

The syntax of if statement is

if (condition)

{

statement 1;

statement 2;

statement n;

}

If the programmer knows the exact number of repetitions to be carried out among the set of statements then ‘for’ conditional statement is used in a program.

The ‘if’ statement is used to decide on whether a statement or a block should be executed or not.

A group of statements separated by semicolons and grouped together and enclosed within brackets marked with { } is called a block.

The control statements are classified as

1. Selection statements

2. Iterative statements

3. Jump statements.

Control statements are elements in the program that can control and alter the sequence of flow of constructions in any program execution.

The execution of a program can be stopped at any point with ‘exit ( )’ and a status code can be informed to the calling program.

A compound statement is a grouping of statements enclosed within a pair of braces ({ }), in which each individual statement ends with a semicolon.

The ‘continue’ statement is used in loops and causes a program to skip the rest of the body of the loop.

The ‘go to’ statement transfers/jump control from one part of the program to some other part.

An if statement nestling inside another ‘if’ statement is termed as ‘a nested if’ statement.

The other name of ‘if’ statement is one-way branching statement.

The multi-branch selection statement is called as ‘switch-case’ statement.

The numerical equivalent of TRUE is 1 and FALSE is 0.

The ‘if-else if’ statement is an extension of the “if-else” conditional branching statement. When the expression in the “if’ condition is “false” another “if-else” construct is used to execute a set statement based on an expression.

‘If else’ statement is a conditional branching statement used to execute a set of codes when the condition is true, otherwise executes a different set of the codes in the “else” part.

The other name of ‘if-else’ statement is two-way branching.

The possible output of condition evaluation is either TRUE or FALSE.

The ‘break’ statement can be used to terminate a repeated structure (loops) such as ‘while’, do-while ‘and’ ‘for’ and multi-branching statements like ‘switch’.

If the loop appears inside the body of another loop it is called a nested loop.

The ‘switch’ statement is used in C++ for testing whether a variable is equal to any one of a set of values.

Control statements are elements in the program that control the flow of program execution. Control statements are classified as,

1. Selection statements

2. Iterative statements

3. Jump statements

Syntax :

switch(expression)

{

case constant 1 :

statements

break

case constant 2 :

statements

break

.

.

default

statements

}

The ‘if-else’ statements permit two-way branching, whereas ‘switch’ statement permits multiple branching.

A ‘switch’ statement allows a variable to be tested for equality against a list of values. Each value is called a case, and the variable being switched on is checked for each case.

Syntax:

The syntax for a switch statement: switch(expression)

{

case constant-expression : statement(s);

break; //optional

case constant-expression : statement(s);

break; //optional

default : statement(s); //Optional

}

The following rules apply to a switch statement:

1. The expression used in a ‘switch’ statement must have an integer or enumerated type.

2. We can have any number of case statements within a ‘switch’. Each case is followed by the value to be compared to, and a colon.

3. The constant-expression for a case must be the same data type as the variable in the ‘switch’, and it must be a constant or a literal.

4. When the variable being switched on is equal to a case, the statements following that case will execute until a ‘break’ statement is reached.

5. When a ‘break’ statement is reached, the ‘switch’ terminates, and the flow of control jumps to the next line following the ‘ switch ’ statement.

6. Not every case needs to contain a break. If no break appears, the flow of control will fall through to subsequent cases until a ‘break’ is reached.

7. If no conditions match, then the code under the default statement is executed.

8. The default case is used for performing a task when none of the cases is ‘true’.

9. No break is needed in the default case.

Example for ‘if’ statement:

# include <iostream.h>

void main ()

{

int a = 100;

int b = 200;

if (b > a)

{

cout <<"B is greater than A";

}

}

Result:

B is greater than A In the above example the condition in the if statement returns a true value and so the text “B is greater than A” is displayed. 

Example for ‘if else’ statement:

#include <iostream.h>

void main ()

{

int a = 10;

int b = 20;

if(a>b)

{

cout <<"A is greater than B";

}

else

{

cout <<"B is greater than A";

}

Result: B is greater than A. In the above example, the “if’ condition is false so the code in the “else” part is executed.

The ‘if-else if’ statement is an extension of the “if-else” conditional branching statement. When the expression in the “if’ condition is “false” another “if-else” construct is used to execute a set of statements based on the expression.

Syntax:

if(expression)

{ statements }

else if(expression)

{ statements }

else if(expression)

{ statements }\

Example: for ‘if else if’ statement

#include<iostream.h>

int main (void)

{

int per;

cout<<"Enter your Percentage::";

cin>>per;

If(per>=80)

{

cout<<"passed with Distinction"<<endI;

}

else if(per>=60)

{

cout <<"First Class"<<end1;

}

else if(per>=50)

}

cout<<"Second Class"<<end1;

}

else

{

cout<<"Third Class"<<end1;

}

return 0;

}

Result:

Enter your Percentage::60

First Class

In the above example, the ‘if else if’ statement is used to check multiple conditions based on the percentage of marks got, as input. The user entered percentage as 60, then first condition evaluated and returned with false. This resulted in checking for second if condition and resulted in true which give the print “first class”.

The ‘do-while’ statement is a post-tested looping statement.

The ‘for’ looping statement is called a fixed-execution looping statement.

The ‘while’ loop evaluates the condition in the beginning itself, to select a suitable statement for execution repeatedly. Therefore it is called a pretested looping statement.