C While Loop

Welcome to The Coding College! In this tutorial, we’ll dive into the while loop in C programming, a fundamental construct for executing repetitive tasks efficiently.

What is a while Loop?

A while loop is a control flow statement that allows a block of code to be executed repeatedly, as long as a specified condition is true. It’s ideal when the number of iterations is not known beforehand.

Syntax

while (condition) {
    // Code to execute as long as the condition is true
}

Key Points:

1. Condition: The loop evaluates the condition before executing the code block.
2. Execution: If the condition is true, the code block executes. If false, the loop terminates.
3. Infinite Loop: Ensure the condition eventually becomes false to avoid infinite loops.

Example 1: Print Numbers from 1 to 5

#include <stdio.h>

int main() {
    int i = 1;

    while (i <= 5) {
        printf("%d\n", i);
        i++;
    }

    return 0;
}

Output:

1  
2  
3  
4  
5  

Example 2: Sum of Natural Numbers

#include <stdio.h>

int main() {
    int n, sum = 0, i = 1;

    printf("Enter a positive integer: ");
    scanf("%d", &n);

    while (i <= n) {
        sum += i;
        i++;
    }

    printf("Sum of first %d natural numbers is: %d\n", n, sum);

    return 0;
}

Output:

Enter a positive integer: 5  
Sum of first 5 natural numbers is: 15

Example 3: Check Even or Odd Numbers in a Range

#include <stdio.h>

int main() {
    int start, end;

    printf("Enter start and end of range: ");
    scanf("%d %d", &start, &end);

    printf("Even numbers in the range:\n");
    while (start <= end) {
        if (start % 2 == 0) {
            printf("%d\n", start);
        }
        start++;
    }

    return 0;
}

Output:

Enter start and end of range: 2 10  
Even numbers in the range:  
2  
4  
6  
8  
10  

Handling Infinite Loops

An infinite loop occurs when the condition in a while statement never becomes false. Here’s an example:

#include <stdio.h>

int main() {
    int i = 1;

    while (i <= 5) {
        printf("%d\n", i);
        // Uncomment the next line to avoid an infinite loop
        // i++;
    }

    return 0;
}

Solution: Always update variables involved in the condition to prevent infinite loops.

Use Cases of while Loops

1. Reading User Input: Keep asking for input until it is valid.
2. Processing Data: Work through a dataset or file until the end.
3. Real-Time Monitoring: Continuously check conditions in embedded systems or games.

Best Practices

1. Initialize Variables Properly: Ensure variables in the condition are initialized to avoid undefined behavior.
2. Prevent Infinite Loops: Update the condition variable or include a termination condition within the loop.
3. Keep the Body Simple: Avoid overly complex logic in the loop body for better readability.

Advanced Example: Factorial Calculation

#include <stdio.h>

int main() {
    int num, factorial = 1;

    printf("Enter a positive integer: ");
    scanf("%d", &num);

    int i = 1;
    while (i <= num) {
        factorial *= i;
        i++;
    }

    printf("Factorial of %d is: %d\n", num, factorial);

    return 0;
}

Output:

Enter a positive integer: 5  
Factorial of 5 is: 120

Difference Between while and do...while

Conclusion

The while loop is an essential construct in C programming for handling repetitive tasks where the number of iterations is not predefined. By mastering its usage, you can write efficient and readable code.