Example: Matrix Multiplication in C

// Matrix Multiplication
#include <stdio.h>

int main() {
    int r1, c1, r2, c2;

    // Step 1: Get dimensions for the first matrix
    printf("Enter rows and columns for first matrix (e.g., 2 3): ");
    scanf("%d %d", &r1, &c1);

    // Step 2: Get dimensions for the second matrix
    printf("Enter rows and columns for second matrix (e.g., 3 2): ");
    scanf("%d %d", &r2, &c2);

    // Step 3: Check if multiplication is possible
    if (c1 != r2) {
        printf("Error: Number of columns of first matrix must be equal to number of rows of second matrix.\n");
        return 1; // Indicate an error
    }

    // Declare matrices with max size or dynamic allocation (for simplicity, using fixed large size here)
    // For production, consider dynamic allocation based on r1, c1, r2, c2
    int matrix1[10][10], matrix2[10][10], resultMatrix[10][10];
    int i, j, k;

    // Step 4: Input elements for the first matrix
    printf("\nEnter elements of first matrix:\n");
    for (i = 0; i < r1; ++i) {
        for (j = 0; j < c1; ++j) {
            printf("Enter element matrix1[%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix1[i][j]);
        }
    }

    // Step 5: Input elements for the second matrix
    printf("\nEnter elements of second matrix:\n");
    for (i = 0; i < r2; ++i) {
        for (j = 0; j < c2; ++j) {
            printf("Enter element matrix2[%d][%d]: ", i + 1, j + 1);
            scanf("%d", &matrix2[i][j]);
        }
    }

    // Step 6: Initialize result matrix with zeros
    for (i = 0; i < r1; ++i) {
        for (j = 0; j < c2; ++j) {
            resultMatrix[i][j] = 0;
        }
    }

    // Step 7: Perform matrix multiplication
    // Outer loops iterate through rows of result matrix (r1) and columns of result matrix (c2)
    for (i = 0; i < r1; ++i) { // rows of first matrix
        for (j = 0; j < c2; ++j) { // columns of second matrix
            // Innermost loop calculates the sum of products for each element of the result matrix
            for (k = 0; k < c1; ++k) { // columns of first matrix OR rows of second matrix
                resultMatrix[i][j] += matrix1[i][k] * matrix2[k][j];
            }
        }
    }

    // Step 8: Display the result matrix
    printf("\nResultant matrix after multiplication:\n");
    for (i = 0; i < r1; ++i) {
        for (j = 0; j < c2; ++j) {
            printf("%d ", resultMatrix[i][j]);
        }
        printf("\n");
    }

    return 0;
}