How to Initialize Array in C: Syntax and Examples

In C, you can initialize an array by specifying its elements inside curly braces using int arr[] = {1, 2, 3};. You can also declare the size explicitly like int arr[3] = {1, 2, 3}; or initialize all elements to zero with int arr[5] = {0};.

Syntax

To initialize an array in C, you use the following syntax:

• type arrayName[size] = {value1, value2, ...}; - declares an array with a fixed size and initializes it with values.
• type arrayName[] = {value1, value2, ...}; - declares an array where the size is inferred from the number of values.
• type arrayName[size] = {0}; - initializes all elements to zero.

c

int arr1[3] = {1, 2, 3};
int arr2[] = {4, 5, 6, 7};
int arr3[5] = {0};

Example

This example shows how to declare and initialize arrays, then print their elements.

c

#include <stdio.h>

int main() {
    int numbers[4] = {10, 20, 30, 40};
    int zeros[5] = {0};

    printf("numbers array: ");
    for (int i = 0; i < 4; i++) {
        printf("%d ", numbers[i]);
    }
    printf("\n");

    printf("zeros array: ");
    for (int i = 0; i < 5; i++) {
        printf("%d ", zeros[i]);
    }
    printf("\n");

    return 0;
}

Output

numbers array: 10 20 30 40 
zeros array: 0 0 0 0 0 

Common Pitfalls

Common mistakes when initializing arrays in C include:

• Not specifying enough initial values for the declared size, which leaves some elements uninitialized and may contain garbage values.
• Forgetting to initialize arrays, leading to unpredictable values.
• Using an initializer list larger than the declared size, which causes a compilation error.

Always ensure the number of initial values does not exceed the array size and initialize arrays to avoid garbage data.

c

/* Wrong: initializer list larger than size */
int arr[3] = {1, 2, 3, 4}; // Error

/* Right: initializer list fits size */
int arr[4] = {1, 2, 3, 4};

Quick Reference

Initialization Method	Description	Example
Fixed size with values	Declare size and initialize with values	int arr[3] = {1, 2, 3};
Size inferred	Let compiler count elements	int arr[] = {4, 5, 6};
Zero initialization	Set all elements to zero	int arr[5] = {0};
Partial initialization	Initialize first elements, rest zero	int arr[5] = {1, 2};

Key Takeaways

Initialize arrays using curly braces with values inside.

Array size can be fixed or inferred from initializer list.

Uninitialized elements may contain garbage values; use zero initialization if needed.

Initializer list size must not exceed declared array size.

Partial initialization sets remaining elements to zero automatically.