C do while Loop

Posted in C Tutorial

Updated on Sep 03, 2024

By Mari Selvan

👁️ 34 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

The do while loop in C is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition.

Unlike other loops (for and while), a do while loop will always execute at least once, even if the condition is false.

🤔 What is a do while Loop?

A do while loop is a post-tested loop, meaning the condition is evaluated after the loop body has been executed. This ensures that the loop executes at least once before any condition check is performed.

🔑 Key Features

Guaranteed Execution: The loop body executes at least once, regardless of the condition.
Post-Test Loop: The condition is evaluated after the loop body has been executed.
Flexible Control Flow: Useful for scenarios where the loop body needs to execute before checking the condition.

💡 Syntax

The syntax for the do while loop is as follows:

example.c

Copied

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

Explanation

do: Initiates the loop.
{ }: Contains the code block that will execute.
while (condition): The condition to be tested after the code block executes. If true, the loop repeats; if false, the loop terminates.

Basic Example

Here’s a simple example to illustrate a do while loop:

example.c

Copied

#include <stdio.h>

int main() {
  int i = 0;
  do {
    printf("%d\n", i);
    i++;
  } while (i < 5);
  return 0;
}

💻 Output

In this example, the loop will print the value of i from 0 to 4. The condition i < 5 is evaluated after the loop body executes, ensuring that the body runs at least once.

Output

Practical Usage

The do while loop is particularly useful in scenarios where the loop body must execute at least once, such as:

Input Validation: Prompting user input and validating it in the loop.
Menus: Displaying a menu at least once before repeating based on user choice.

Example: Input Validation

example.c

Copied

#include <stdio.h>

int main() {
  int num;
  do {
    printf("Enter a number between 1 and 10: ");
    scanf("%d", &num);
  } while (num < 1 || num > 10);
  printf("You entered: %d\n", num);
  return 0;
}

In this example, the user is prompted to enter a number between 1 and 10. The loop ensures the prompt appears at least once and repeats until a valid number is entered.

Example: Menu Display

example.c

Copied

#include <stdio.h>

int main() {
  int choice;
  do {
    printf("Menu:\n");
    printf("1. Option 1\n");
    printf("2. Option 2\n");
    printf("3. Exit\n");
    printf("Enter your choice: ");
    scanf("%d", &choice);

    switch (choice) {
      case 1:
        printf("Option 1 selected.\n");
        break;
      case 2:
        printf("Option 2 selected.\n");
        break;
      case 3:
        printf("Exiting...\n");
        break;
      default:
        printf("Invalid choice, please try again.\n");
    }
  } while (choice != 3);
  return 0;
}

In this menu example, the menu is displayed at least once and continues to display until the user selects the exit option.

Common Pitfalls and Best Practices

Infinite Loops:

Be cautious of creating infinite loops with do while. Ensure the condition will eventually become false to terminate the loop.
Condition Placement:

Remember that the condition is checked after the loop body executes. Ensure this behavior aligns with your program's logic.
Clear Conditions:

Write clear and concise conditions to maintain readability and prevent logical errors.

🎉 Conclusion

The do while loop is a valuable control flow statement in C that guarantees the loop body executes at least once.

By understanding its syntax and practical applications, you can effectively use do while loops in your programs to handle scenarios requiring at least one execution before condition checking.