While Loop in C

In this tutorial, we will learn about while loop in C. We will cover the basics of iterative execution using while loops.

What is a While Loop

A while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The loop runs as long as the condition evaluates to true.

Syntax

The syntax for the while loop in C is:

while (condition) {
    // Code block to be executed
}

The while loop evaluates the condition before executing the loop's body. If the condition is true, the code block inside the loop is executed. This process repeats until the condition becomes false.

Flowchart of While Loop

Example 1: Printing Numbers from 1 to 5

  1. Declare an integer variable i.
  2. Initialize i to 1.
  3. Use a while loop to print numbers from 1 to 5.

C Program

#include <stdio.h>
int main() {
    int i = 1;
    while (i <= 5) {
        printf("%d ", i);
        i++;
    }
    return 0;
}

Output

1 2 3 4 5

Example 2: Calculating the Sum of First N Natural Numbers

  1. Declare two integer variables: n and sum.
  2. Assign a value to n.
  3. Initialize sum to 0.
  4. Use a while loop to calculate the sum of the first n natural numbers.
  5. Print the sum.

C Program

#include <stdio.h>
int main() {
    int n = 10;
    int sum = 0;
    int i = 1;
    while (i <= n) {
        sum += i;
        i++;
    }
    printf("Sum of first %d natural numbers is %d\n", n, sum);
    return 0;
}

Output

Sum of first 10 natural numbers is 55

Example 3: Reversing a Number

  1. Declare three integer variables: num, rev, and digit.
  2. Assign a value to num.
  3. Initialize rev to 0.
  4. Use a while loop to reverse the digits of num.
  5. Print the reversed number.

C Program

#include <stdio.h>
int main() {
    int num = 12345;
    int rev = 0;
    while (num != 0) {
        int digit = num % 10;
        rev = rev * 10 + digit;
        num /= 10;
    }
    printf("Reversed number is %d\n", rev);
    return 0;
}

Output

Reversed number is 54321