C program to multiply two matrices

The below program multiplies two square matrices of size 4*4, we can change N for different dimension.

#include <stdio.h> #define N 4   // This function multiplies A[][] and B[][], and stores // the result in C[][] void multiply(int A[][N], int B[][N], int C[][N]) {     int i, j, k;     for (i = 0; i < N; i++)     {         for (j = 0; j < N; j++)         {             C[i][j] = 0;             for (k = 0; k < N; k++)                 C[i][j] += A[i][k]*B[k][j];         }     } }   int main() {     int A[N][N] = { {1, 1, 1, 1},                     {2, 2, 2, 2},                     {3, 3, 3, 3},                     {4, 4, 4, 4}};       int B[N][N] = { {1, 1, 1, 1},                     {2, 2, 2, 2},                     {3, 3, 3, 3},                     {4, 4, 4, 4}};       int C[N][N]; // To store result     int i, j;     multiply(A, B, C);       printf("Result matrix is \n");     for (i = 0; i < N; i++)     {         for (j = 0; j < N; j++)            printf("%d ", C[i][j]);         printf("\n");     }       return 0; }

Output:

Result matrix is
10 10 10 10
20 20 20 20
30 30 30 30
40 40 40 40 

The program can be extended for rectangular matrices. The following post can be useful for extending this program.

How to pass a 2D array as a parameter in C?

The time complexity of the above program is O(n3). It can be optimized using Strassen’s Matrix Multiplication

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