Declare and Initialize a 2D Array in C

In C, a 2D array is an array of arrays, meaning it consists of multiple rows and columns. A 2D array is declared using two sets of square brackets [rows][columns]. It can be initialized at the time of declaration or later using loops.

In this tutorial, we will cover different ways to declare and initialize a 2D array with examples.

Examples of Declaring and Initializing a 2D Array

1. Declaring and Initializing a 2D Array at the Time of Declaration

In this example, we will declare and initialize a 2D array at the time of its definition.

main.c

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#include <stdio.h>

int main() {
    // Declaring and initializing a 2D array
    int matrix[2][3] = {
        {1, 2, 3},
        {4, 5, 6}
    };

    // Printing the 2D array elements
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", matrix[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Explanation:

  1. We declare a 2D array matrix[2][3] with 2 rows and 3 columns.
  2. We initialize the array with predefined values using curly braces {}.
  3. Using nested for loops, we iterate over each row (i) and column (j).
  4. The inner loop prints each element followed by a space, while the outer loop prints a new line after each row.

Output:

1 2 3 
4 5 6

2. Initializing a 2D Array Using Loops

In this example, we will initialize a 2D array using nested loops and user input.

main.c

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#include <stdio.h>

int main() {
    int matrix[2][2];

    // Taking user input to initialize the 2D array
    printf("Enter 4 elements for the 2x2 matrix:\n");
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            scanf("%d", &matrix[i][j]);
        }
    }

    // Printing the 2D array
    printf("The entered matrix is:\n");
    for (int i = 0; i < 2; i++) {
        for (int j = 0; j < 2; j++) {
            printf("%d ", matrix[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Explanation:

  1. We declare a 2D array matrix[2][2] without initializing it.
  2. Using nested loops, we take user input to fill the array.
  3. The scanf() function reads user input and stores it in matrix[i][j].
  4. Another nested loop is used to print the matrix in the correct format.

Output (Example User Input: 1 2 3 4):

Enter 4 elements for the 2x2 matrix:
1 2
3 4
The entered matrix is:
1 2
3 4

3. Declaring and Initializing a 2D Array with Partial Initialization

In this example, we will see how a 2D array behaves when it is partially initialized.

main.c

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#include <stdio.h>

int main() {
    // Partially initialized 2D array
    int matrix[3][3] = {
        {1, 2}, 
        {3}, 
        {4, 5, 6}
    };

    // Printing the array
    for (int i = 0; i < 3; i++) {
        for (int j = 0; j < 3; j++) {
            printf("%d ", matrix[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Explanation:

  1. We declare a 3x3 matrix but initialize only some elements.
  2. Missing elements are automatically set to 0 by default.
  3. We use nested loops to print the matrix.

Output:

1 2 0 
3 0 0 
4 5 6

Conclusion

In this tutorial, we explored different ways to declare and initialize a 2D array in C:

  1. Direct Initialization: Assigning values while declaring the array.
  2. Loop Initialization: Taking input using loops and assigning values dynamically.
  3. Partial Initialization: Initializing only some elements, with others defaulting to zero.