All programming languages offers loop control structure (also known as looping) allowing programmers to execute a statement or group of statements multiple times.
In looping, the sequences of statements are executed until some exit condition is satisfied. The looping construct is composed of two parts: body of loop and control statement.
In entry controlled loop the exit/control condition is checked before executions of statements inside loop body.
In exit controlled loop the exit/control condition is checked after executions of loop body.
This means that in case of exit controlled loop, body will be executed at least once before exiting from the loop.4
for
while
do...while
The For Loop
The for loop is normally used when we want to execute block of statements fixed number of times. To make for loop more dynamic, we can use the exit condition inside for loop.
Syntax of For Loop for ( expression1; expression2; expression3)
The header of for loop contains three expressions separated by semicolons in parenthesis. All these expressions are optional. Statement-block which is also known as body of for loop may contain simple statement or compound statement.
The While Loop
When number of iteration cannot be pre-determined and when loop terminating condition is to be tested before entering the loop, at that time use of while loop is more suitable.
The do-while loop
While loop, the test expression is checked before executing body of loop. The do...while loop should be used when the test expression is to be checked after executing body of loop. As we are checking test condition at the end of loop, the do...while loop is a kind of exit-controlled loop.
The Infinite Loop Any loop in a program becomes infinite loop if it runs forever and program control never comes out of it. The loop becomes infinite due to non availability of exit condition in the logic of loop.
int main ()
for(;;)
printf(" This for loop will run forever..... \n");
Choose the correct option from the following:
(1) How many times printf statement is executed in the following program segment ?
int num1 = 3, num2 = 6;
while(numl < num2) {
printf(" Hello Students...");
num1 = numl + 1;
(a) 1
(b) 2
(c) 3
(d) 6
(2) What is the output of following program segment ?
int a = 5, b = 10;
do
a = a + 1;
}while( a < = b); printf(" %d", a);
(a) 10
(b) 9
(c) 11
(d) 15
(3) What is the output of following program segment ?
int main(){
int i;
for(i = 0; i < 10; i++);
printf("%d", i);
(a) 0123456789
(b) 9
(c) 10
(d) Error
(4) What is the value of a number variable after execution of following code ?
int number = 1; while(number <5){
number = number + 1; if( number = = 3) {
continue;
(a) 1
(b) 3
(c) 5
(d) None of these