Initialization of a multidimensional arrays in C/C++

Multidimensional arrays in C are arrays of arrays, where each element is itself an array. They are used to represent data in multiple dimensions like matrices, tables, or grids. The most common type is a 2D array, but C supports arrays of any dimension.

Syntax

// Declaration and initialization
data_type array_name[size1][size2]...[sizeN] = {
    {{values}, {values}},
    {{values}, {values}}
};

// Or with partial initialization
data_type array_name[size1][size2] = {{val1, val2}, {val3, val4}};

Example 1: 2D Array Initialization

Here's how to initialize and work with a 2D array in C −

#include <stdio.h>

int main() {
    int arr[2][3] = {{1, 2, 3}, {4, 5, 6}};
    
    printf("Size of the array: %zu bytes\n", sizeof(arr));
    printf("Content of the 2D array:\n");
    
    for(int i = 0; i < 2; i++) {
        for(int j = 0; j < 3; j++) {
            printf("%d ", arr[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}

Size of the array: 24 bytes
Content of the 2D array:
1 2 3 
4 5 6 

Example 2: 3D Array Initialization

This example demonstrates initializing a 3D array with explicit values −

#include <stdio.h>

int main() {
    int arr[2][2][2] = {
        {{1, 2}, {3, 4}},
        {{5, 6}, {7, 8}}
    };
    
    printf("3D Array content:\n");
    for(int i = 0; i < 2; i++) {
        printf("Layer %d:\n", i);
        for(int j = 0; j < 2; j++) {
            for(int k = 0; k < 2; k++) {
                printf("arr[%d][%d][%d] = %d  ", i, j, k, arr[i][j][k]);
            }
            printf("\n");
        }
        printf("\n");
    }
    
    return 0;
}

3D Array content:
Layer 0:
arr[0][0][0] = 1  arr[0][0][1] = 2  
arr[0][1][0] = 3  arr[0][1][1] = 4  

Layer 1:
arr[1][0][0] = 5  arr[1][0][1] = 6  
arr[1][1][0] = 7  arr[1][1][1] = 8  

Example 3: Partial Initialization

You can initialize only some elements, and the rest will be set to zero −

#include <stdio.h>

int main() {
    int arr[3][3] = {{1, 2}, {3}};  /* Partial initialization */
    
    printf("Partially initialized array:\n");
    for(int i = 0; i < 3; i++) {
        for(int j = 0; j < 3; j++) {
            printf("%d ", arr[i][j]);
        }
        printf("\n");
    }
    
    return 0;
}

Partially initialized array:
1 2 0 
3 0 0 
0 0 0 

Key Points

• In array declaration like int arr[2][3], the first dimension can be omitted during initialization: int arr[][3] = {...}
• All dimensions except the first must be specified in function parameters
• Memory is allocated contiguously in row-major order
• Uninitialized elements are automatically set to zero

Conclusion

Multidimensional arrays in C provide an efficient way to store and manipulate structured data. Proper initialization ensures predictable behavior and optimal memory usage in your programs.