Matrix Addition and Subtraction in C

Two matrices can be added or subtracted only when they have the same number of rows and columns. Each result element is calculated from the elements at the same row and column in the two input matrices.

Add Two 2 × 2 Matrices Top ↑

#include <stdio.h>

int main(void) {
    int first[2][2] = {
        {1, 2},
        {3, 4}
    };

    int second[2][2] = {
        {5, 6},
        {7, 8}
    };

    int sum[2][2];

    for (int row = 0; row < 2; row++) {
        for (int column = 0; column < 2; column++) {
            sum[row][column] =
                first[row][column] + second[row][column];
        }
    }

    for (int row = 0; row < 2; row++) {
        for (int column = 0; column < 2; column++) {
            printf("%4d", sum[row][column]);
        }
        putchar('\n');
    }

    return 0;
}

Output

6   8
10  12

Add Two 3 × 3 Matrices Top ↑

#include <stdio.h>

int main(void) {
    int first[3][3] = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
    };

    int second[3][3] = {
        {10, 20, 30},
        {40, 50, 60},
        {70, 80, 90}
    };

    int sum[3][3];

    for (int row = 0; row < 3; row++) {
        for (int column = 0; column < 3; column++) {
            sum[row][column] =
                first[row][column] + second[row][column];
        }
    }

    for (int row = 0; row < 3; row++) {
        for (int column = 0; column < 3; column++) {
            printf("%d ", sum[row][column]);
        }
        putchar('\n');
    }

    return 0;
}

Output

11 22 33
44 55 66
77 88 99

Matrix Subtraction Top ↑

Key change: replace the addition operator with subtraction:

difference[row][column] =
    first[row][column] - second[row][column];

User-Entered Matrix Addition Top ↑

#include <stdio.h>

#define MAX 10

int main(void) {
    int rows;
    int columns;
    int first[MAX][MAX];
    int second[MAX][MAX];
    int sum[MAX][MAX];

    printf("Enter rows and columns (1..10): ");
    if (scanf("%d %d", &rows, &columns) != 2 ||
        rows < 1 || rows > MAX ||
        columns < 1 || columns > MAX) {
        printf("Invalid matrix size.\n");
        return 1;
    }

    printf("Enter first matrix:\n");
    for (int row = 0; row < rows; row++) {
        for (int column = 0; column < columns; column++) {
            if (scanf("%d", &first[row][column]) != 1) {
                printf("Invalid input.\n");
                return 1;
            }
        }
    }

    printf("Enter second matrix:\n");
    for (int row = 0; row < rows; row++) {
        for (int column = 0; column < columns; column++) {
            if (scanf("%d", &second[row][column]) != 1) {
                printf("Invalid input.\n");
                return 1;
            }
        }
    }

    for (int row = 0; row < rows; row++) {
        for (int column = 0; column < columns; column++) {
            sum[row][column] =
                first[row][column] + second[row][column];
        }
    }

    printf("Sum matrix:\n");
    for (int row = 0; row < rows; row++) {
        for (int column = 0; column < columns; column++) {
            printf("%d ", sum[row][column]);
        }
        putchar('\n');
    }

    return 0;
}

Why the Dimensions Must Match Top ↑

Addition and subtraction operate element by element. Therefore both input matrices must have the same shape. Matrix multiplication follows a different compatibility rule; see matrix multiplication in C.

Subhendu Mohapatra

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