Understanding the auto Keyword in C

C Programming @ Freshers.in

In C programming, the ‘auto’ keyword is one of the less commonly used keywords, but it plays a crucial role in variable declaration and storage duration. In this article, we will explain the ‘auto’ keyword, its purpose, and provide real-world examples to illustrate its usage.

The ‘auto’ Keyword in C

The ‘auto’ keyword in C is primarily used to declare local variables with automatic storage duration. Variables declared with ‘auto’ are automatically allocated and deallocated within their scope, making them the default type for local variables.


auto data_type variable_name = initial_value;

Example 1: Basic Usage of ‘auto’

#include <stdio.h>
int main() {
    auto int x = 42;
    printf("The value of x is %d\n", x);
    return 0;


The value of x is 42

In this example, we declare an integer variable x using the ‘auto’ keyword. The variable is assigned the value 42 and is automatically allocated in the local scope of the main function.

Automatic Storage Duration

Variables declared with ‘auto’ have automatic storage duration, meaning they are created when the program enters their scope and destroyed when the program exits that scope. This is the default behavior for local variables in C.

Example 2: Automatic Storage Duration

#include <stdio.h>
void someFunction() {
    auto int y = 10;
    printf("The value of y is %d\n", y);
int main() {
    // y is automatically destroyed here
    return 0;


The value of y is 10

In this example, the variable y is created when someFunction is called and destroyed when it exits. This demonstrates the automatic storage duration of ‘auto’ variables.

Use Cases for ‘auto’

  1. Legacy Usage: In modern C programming, the ‘auto’ keyword is rarely used, as local variables are automatically assumed to have automatic storage duration. It’s more commonly seen in older C code.
  2. Readability: Some programmers use ‘auto’ for improved code readability, but it’s not required.
Author: user