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Variable Length Arrays (VLAs) in C

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In C, variable length arrays (VLAs) are also known as runtime-sized variable-sized or variable-sized arrays. The size of such arrays is defined at run-time.

Variably modified types include variable-length arrays and pointers to variable-length arrays. Variably changed types must be declared at either block scope or function prototype scope.

Variable length arrays are a feature where we can allocate an auto array (on stack) of variable size. It can be used in a typedef statement. C supports variable-sized arrays from the C99 standard. For example, the below program compiles and runs fine in C.

Syntax of VLAs in C

void fun(int size)
{
int arr[size];
// code
}

Note: In C99 or C11 standards, there is a feature called flexible array members, which works the same as the above. 

Example of Variable Length Arrays

The below example shows the implementation of variable length arrays in C program

C

// C program to demonstrate variable length array
#include <stdio.h>
 
// function to initialize array
void initialize(int* arr, int size)
{
    for (int i = 0; i < size; i++) {
        arr[i] = i + 1;
    }
}
 
// function to print an array
void printArray(int size)
{
    // variable length array
    int arr[size];
    initialize(arr, size);
 
    for (int i = 0; i < size; i++) {
        printf("%d ", arr[i]);
    }
}
 
// driver code
int main()
{
    int n = 5;
    printArray(n);
 
    return 0;
}

                    

Output
1 2 3 4 5 

Explanation: The above program illustrate how to create a variable size array in a function in C program. This size is passed as parameter and the variable array is created on the stack memory.


Last Updated : 08 Jan, 2024
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