Example: Matrix Multiplication using Pointers in C

// Matrix Multiplication using Pointers
#include <stdio.h>   // For input/output operations (printf, scanf)
#include <stdlib.h>  // For dynamic memory allocation (malloc, free)

// Function to allocate memory for a matrix
int** allocateMatrix(int rows, int cols) {
    int** matrix = (int**)malloc(rows * sizeof(int*)); // Allocate memory for rows
    if (matrix == NULL) {
        printf("Memory allocation failed for matrix rows!\n");
        exit(1); // Exit if allocation fails
    }
    for (int i = 0; i < rows; i++) {
        matrix[i] = (int*)malloc(cols * sizeof(int)); // Allocate memory for columns in each row
        if (matrix[i] == NULL) {
            printf("Memory allocation failed for matrix columns!\n");
            // Free previously allocated row pointers before exiting
            for (int j = 0; j < i; j++) {
                free(matrix[j]);
            }
            free(matrix);
            exit(1);
        }
    }
    return matrix;
}

// Function to free memory allocated for a matrix
void freeMatrix(int** matrix, int rows) {
    for (int i = 0; i < rows; i++) {
        free(matrix[i]); // Free memory for each row
    }
    free(matrix); // Free memory for the array of row pointers
}

// Function to read matrix elements from user
void readMatrix(int** matrix, int rows, int cols, char name) {
    printf("Enter elements for Matrix %c (%dx%d):\n", name, rows, cols);
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("Enter element [%d][%d]: ", i, j);
            scanf("%d", &matrix[i][j]);
        }
    }
}

// Function to print a matrix
void printMatrix(int** matrix, int rows, int cols, char name) {
    printf("\nMatrix %c (%dx%d):\n", name, rows, cols);
    for (int i = 0; i < rows; i++) {
        for (int j = 0; j < cols; j++) {
            printf("%5d ", matrix[i][j]);
        }
        printf("\n");
    }
}

int main() {
    int rows1, cols1, rows2, cols2;

    // Step 1: Get dimensions for Matrix A from user
    printf("Enter dimensions for Matrix A (rows cols): ");
    scanf("%d %d", &rows1, &cols1);

    // Step 2: Get dimensions for Matrix B from user
    printf("Enter dimensions for Matrix B (rows cols): ");
    scanf("%d %d", &rows2, &cols2);

    // Step 3: Check if multiplication is possible
    if (cols1 != rows2) {
        printf("Error: Number of columns in Matrix A must be equal to number of rows in Matrix B.\n");
        return 1; // Indicate error
    }

    // Step 4: Dynamically allocate memory for matrices
    int** matrixA = allocateMatrix(rows1, cols1);
    int** matrixB = allocateMatrix(rows2, cols2);
    int** resultMatrix = allocateMatrix(rows1, cols2); // Result matrix will be rows1 x cols2

    // Step 5: Read elements for Matrix A and Matrix B
    readMatrix(matrixA, rows1, cols1, 'A');
    readMatrix(matrixB, rows2, cols2, 'B');

    // Step 6: Print original matrices
    printMatrix(matrixA, rows1, cols1, 'A');
    printMatrix(matrixB, rows2, cols2, 'B');

    // Step 7: Perform matrix multiplication
    printf("\nPerforming matrix multiplication...\n");
    for (int i = 0; i < rows1; i++) {
        for (int j = 0; j < cols2; j++) {
            resultMatrix[i][j] = 0; // Initialize element
            for (int k = 0; k < cols1; k++) { // Or k < rows2, since cols1 == rows2
                resultMatrix[i][j] += matrixA[i][k] * matrixB[k][j];
            }
        }
    }

    // Step 8: Print the result matrix
    printMatrix(resultMatrix, rows1, cols2, 'C'); // C for result

    // Step 9: Free allocated memory
    freeMatrix(matrixA, rows1);
    freeMatrix(matrixB, rows2);
    freeMatrix(resultMatrix, rows1);
    printf("\nMemory deallocated successfully.\n");

    return 0; // Indicate successful execution
}