Created: 2023-01-11 17:13
Status: #concept
Subject: Programming
Tags: C Variable Block Scope Scope Global Scope

Local Variable

A kind of variable with Automatic Storage Duration & Block Scope.

These variables are only usable WITHIN { } a specific Function scope or Compound Statement and will be deallocated once the function body terminates.

int sum_digits(int n)\
{
	int sum = 0; // local variable
	
	while (n > 0)
	{
		sum += n % 10; 
		n /= 10;
	}
	
	return sum;
}

What happens when we return the address of an auto local variable from a Function?

The variable scoped to the function will get deallocated when the function exits, leading to the Pointer pointing to an invalid Memory Address.

compilers will warn you, otherwise it will create a Segmentation Fault.

The `static` Keyword

Using the static keyword to declare a variable will make a variable's storage duration Static instead of auto.

this means that storage is not deallocated when the Block Scope collapses.

#include <stdio.h>

int main(void)
{
    count_down();
}

void count_down(void)
{
    static int x = 10; // static declaration
    
    if (x == 0) return; // base case
    else
    {
        printf("%d ", x--); // decrement
        count_down();
    }
}

10 9 8 7 6 5 4 3 2 1

References

C Programming, A Modern Approach, 2nd Edition, Chapter 10.1