C while Loop

Posted in C Tutorial

Updated on Sep 13, 2024

By Mari Selvan

👁️ 60 - Views

⏳ 4 mins

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Photo Credit to CodeToFun

🙋 Introduction

The while loop in C is a fundamental control structure used to repeat a block of code as long as a specified condition remains true.

This guide will provide an in-depth look at how the while loop works, its syntax, and practical examples of its usage.

🤔 What is a while Loop?

In C programming, a while loop is used to execute a block of code repeatedly as long as a given condition evaluates to true. The condition is evaluated before the execution of the loop’s body, making it a pre-test loop.

🔑 Key Features

Pre-test Loop: The condition is evaluated before executing the loop body.
Flexible Control: Can handle complex conditions and dynamic ranges.
Used for Unknown Iterations: Ideal when the number of iterations is not known beforehand.

💡 Syntax

The syntax for the while loop is straightforward:

Syntax

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

🧠 Explanation:

condition: A boolean expression that is evaluated before each iteration. If the condition is true, the loop body is executed. If false, the loop terminates.
{ // Code to be executed }: The block of code that runs repeatedly as long as the condition is true.

Basic Example

Here's a simple example of a while loop that prints numbers from 1 to 5:

example.c

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#include <stdio.h>

int main() {
  int i = 1;
  while (i <= 5) {

    printf("%d\n", i);
    i++;
  }
  return 0;
}

Explanation:

The variable i is initialized to 1.
The while loop checks if i is less than or equal to 5.
If true, it prints the value of i and then increments i by 1.
This process repeats until i is greater than 5.

Infinite while Loop

An infinite loop is a loop that runs indefinitely because the condition never becomes false. Here’s an example of an infinite while loop:

example.c

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#include <stdio.h>

int main() {
  while (1) {
    printf("This is an infinite loop\n");
  }
  return 0;
}

🧠 Explanation

The condition 1 (which is always true) causes the loop to run forever.
Infinite loops are generally used for programs that need to run continuously, such as servers or embedded systems, but should be used with caution to avoid unintentional infinite loops.

while Loop with User Input

Here's an example of using a while loop to repeatedly prompt the user for input until they enter a specific value:

example.c

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#include <stdio.h>

int main() {
  int number;
  
  printf("Enter a number (0 to exit): ");
  scanf("%d", &number);
  
  while (number != 0) {
    printf("You entered: %d\n", number);
    printf("Enter a number (0 to exit): ");
    scanf("%d", &number);
  }
  
  printf("Exited the loop.\n");
  return 0;
}

🧠 Explanation:

The user is prompted to enter a number.
The while loop continues to execute as long as the entered number is not 0.
If the user enters 0, the loop terminates.

Nested while Loops

You can nest while loops within each other to handle more complex scenarios. Here’s an example:

example.c

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#include <stdio.h>

int main() {
  int i = 1;
  while (i <= 3) {
    int j = 1;
    while (j <= 2) {
      printf("i = %d, j = %d\n", i, j);
      j++;
    }
    i++;
  }
  return 0;
}

🧠 Explanation:

The outer loop runs while i is less than or equal to 3.
The inner loop runs while j is less than or equal to 2.
This results in a total of 6 iterations (3 outer * 2 inner).

📚 Common Pitfalls and Best Practices

Ensure Termination:

Always ensure that the condition will eventually become false to avoid infinite loops unless intentionally creating one.
Update Variables Inside the Loop:

Ensure that variables affecting the loop condition are updated within the loop to avoid infinite loops.
Clear and Maintainable Conditions:

Keep loop conditions simple and clear to improve readability and maintainability of your code.