Loops in C programming - Computer science fundamentals tutorial

Loop control structure

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Loop control structure consist of two parts. the two parts are a body of loop and control statement. Loop control structure are used to execute and repeat a block of statement depending on value of a condition

There are three types of loop control statement-

1. For loop.

2. While loop.

3. Do - while loop.

1. for loop: - The For loop provides a mechanism to repeat a task until a particular condition is true. For loop is usually known as determinate or definite loop because the programmer knows exactly how many times the loop will repeat. The number of times the loop has to be executed can be determined mathematically by checking the logic of the loop.

Syntax of for loop : -

For(initialcondition;<endcondition>;increment/decrement)

{

   Statement block;
}

Example of For loop: -

Explanation of this program: -

Here we can see in For loop, loop started from i=0.

Its end condition is i<10.

In this loop it started execute from i=0. After first iteration it incremented to one and repeat same task and print ‘hello’ second time. It continue to execute until initial condition greater than 10.when it greater than 10 loop stop execute

Output: -

While loop: - The while loop provides a mechanism to repeat one or more statements while a particular condition is true.

Syntax of while loop: -

Statement x;

While(condition)

{

  Statement block;

}

Statement y;

Example of while loop: -

Explanation of this program:-

At first initialize i=1.

Then started while loop with ’i<=10’ condition.

Initially i=1 and is less than 10,i.e. condition is true,so in the loop the value i is printed and condition is update so that with every execution of the loop. The loop execute until value of  i greater than equal to 10.

Output: -

Do-while loop:-

The do – while loop is similar to the while loop. The only difference is that in a do-while loop, the test condition evaluated at the end of the loop. Now that the test condition is evaluated at the end which means that the body of the loop gets executed at least one time even condition is false.

Syntax of the Do-while loop: -

statement x;

do

{

  statement block;

}while(condition);

statement y;

Example of Do-while loop: -

Output: -

The major disadvantage of Do-while loop is that always execute at least once, even if the user enters some invalid data, the loop will execute.

Comparison of loop structure statements: -

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