Array initialization assigns initial values to array elements when the array is declared. C supports initializing all elements, initializing selected elements, and allowing the compiler to determine the array size from the initializer.

#include <stdio.h>

int main(void)
{
    int numbers[5] = {10, 20, 30, 40, 50};
    int values[5] = {1, 2};
    int scores[] = {75, 85, 95};

    for (int i = 0; i < 5; i++)
    {
        printf("%d ", numbers[i]);
    }

    printf("\n");

    for (int i = 0; i < 5; i++)
    {
        printf("%d ", values[i]);
    }

    printf("\n");

    for (int i = 0; i < 3; i++)
    {
        printf("%d ", scores[i]);
    }

    printf("\n");

    return 0;
}

Example Output #

10 20 30 40 50
1 2 0 0 0
75 85 95

Explanation #

The declaration:

int numbers[5] = {10, 20, 30, 40, 50};

initializes all five elements with the specified values.

When an array is partially initialized, the remaining elements are initialized to zero:

int values[5] = {1, 2};

The resulting elements are {1, 2, 0, 0, 0}.

When the array size is omitted, the compiler determines the number of elements from the initializer:

int scores[] = {75, 85, 95};

This declaration creates an array containing three elements.

Array Initialization Forms #

Designated initializers can initialize specific indices:

int numbers[5] = {
    [0] = 10,
    [3] = 40
};

The resulting array is {10, 0, 0, 40, 0}. Designated initializers are supported in C99 and later.

Array initialization occurs as part of the declaration. Ordinary arrays cannot be initialized later using an assignment-style initializer; individual elements must be assigned separately.