Question

I’m trying to solve a matrix multiplication problem with C. Matrix sizes given in problem (2×2)
I wrote this code but it doesn’t print result as I expect. I think I’m missing a point about rules of C.

What is my mistake in this code ?

#include <stdio.h>
int main() {
    int matA[2][2]={0,1,2,3};
    int matB[2][2]={0,1,2,3};
    int matC[2][2];
    int i, j, k;
    for (i = 0; i < 2; i++) {
        for(j = 0; j < 2; j++) {
            for(k = 0; k < 2; k++) {
                matC[i][j] += matA[i][k] * matB[k][j];
            }
            printf("%d\n",matC[i][j]);
        } 
    }
}

Printing Result:

2 
3 
4195350
11

Answer 1

The problem is that in the line

matC[i][j] += matA[i][k] * matB[k][j];

you are adding things to matC, but when you create it, you don’t initialize it, so it has garbage.

You sould do something like:

int matC[2][2] = {0} which will initialize all the matrix with 0’s