C program to multiply two matrix using pointers

Write a C program to multiply two matrix using pointers. How to input and multiply two matrix using pointer in C programming. Logic to multiply two matrix using pointer in C.

Input elements of matrix1:
10 20 30
40 50 60
70 80 90
Input elements of matrix2:
1 2 3
4 5 6
7 8 9

Product of matrices is :
300 360 420
660 810 960
1020 1260 1500

Required knowledge

Functions, Array, Pointers, Pointer and Arrays

How to multiply two matrices?

Multiplication of two matrices is defined only if columns of first matrix is equal to rows of second matrix. Multiplication of two matrices is defined by

How to multiply two matrix using pointers?

In previous posts we learned to access a multi-dimensional array using pointer. Here in this post we will continue our learning further and learn to multiply two matrices using pointers.

Logic of this program won’t be any different from the program to multiply two matrix using array notation. In this post I will explain how to convert array notation of matrix multiplication to pointer notation. Which will help in boosting your pointer knowledge.

In array notation to multiply two matrix we use sum += A[row][i] * B[i][col]; which in pointer notation is equivalent to sum += (*(*(A + row) + i)) * (*(*(B + i) + col));

Program to multiply two matrix using pointers?

/**
 * C program to multiply two matrix using pointers
 */

#include <stdio.h>

#define ROW 3
#define COL 3


/* Function declarations */
void matrixInput(int mat[][COL]);
void matrixPrint(int mat[][COL]);
void matrixMultiply(int mat1[][COL], int mat2[][COL], int res[][COL]);



int main()
{
    int mat1[ROW][COL];
    int mat2[ROW][COL];
    int product[ROW][COL];


    /*
     * Input elements in matrices.
     */
    printf("Enter elements in first matrix of size %dx%d\n", ROW, COL);
    matrixInput(mat1);

    printf("Enter elements in second matrix of size %dx%d\n", ROW, COL);
    matrixInput(mat2);


    // Call function to multiply both matrices
    matrixMultiply(mat1, mat2, product);


    // Print product of both matrix
    printf("Product of both matrices is : \n");
    matrixPrint(product);

    return 0;
}



/**
 * Function to input elements in matrix from user.
 *
 * @mat     Two-dimensional array to store user input.
 */
void matrixInput(int mat[][COL])
{
    int row, col;

    for (row = 0; row < ROW; row++)
    {
        for (col = 0; col < COL; col++)
        {
            scanf("%d", (*(mat + row) + col));
        }
    }
}




/**
 * Function to print elements in a two-dimensional array.
 *
 * @mat     Two-dimensional array to print.
 */
void matrixPrint(int mat[][COL])
{
    int row, col;

    for (row = 0; row < ROW; row++)
    {
        for (col = 0; col < COL; col++)
        {
            printf("%d ", *(*(mat + row) + col));
        }

        printf("\n");
    }
}




/**
 * Function to multiply two matrices.
 *
 * @mat1    First matrix
 * @mat2    Second matrix
 * @res     Resultant matrix to store product of both matrices.
 */
void matrixMultiply(int mat1[][COL], int mat2[][COL], int res[][COL])
{
    int row, col, i;
    int sum;


    for (row = 0; row < ROW; row++)
    {
        for (col = 0; col < COL; col++)
        {
            sum = 0;

            /*
             * Find sum of product of each elements of 
             * rows of first matrix and columns of second 
             * matrix.
             */
            for (i = 0; i < COL; i++)
            {
                sum += (*(*(mat1 + row) + i)) * (*(*(mat2 + i) + col));
            }


            /* 
             * Store sum of product of row of first matrix 
             * and column of second matrix to resultant matrix.
             */
            *(*(res + row) + col) = sum;
        }
    }
}

Enter elements in first matrix of size 3x3
10 20 30
40 50 60
70 80 90
Enter elements in second matrix of size 3x3
1 2 3
4 5 6
7 8 9
Product of both matrices is :
300 360 420
660 810 960
1020 1260 1500