Matrix-Multiplication in C not working properly

Question

I want to create a function for matrix multiplication in C. To this end I defined the function matrix_mult().

When I call this function with the following parameters:

int matrix1[l][m] = {{1,2}, {1,2}};
int matrix2[m][k] = {{1,0}, {0,1}};

in the main() method like so:

int main()
{
    int matrix1[l][m] = {{1,2}, {1,2}};
    int matrix2[m][k] = {{1,0}, {0,1}};
    matrix_mult(matrix1, matrix2);

    return 0;
}

I get the following result:

59 59 
68 60 

The correct result would be:

1  2
1  2

I just don't get what the code is doing wrong.

The definition of the function matrix_mult() is given below:

#define l 2
#define m 2
#define k 2

int matrix_mult(int m1[l][m], int m2[m][k]) {

    int res[l][k];
    for(int row=0;row<l;row++){
        for (int col=0;col<k;col++){
            for(int j=0;j<m;j++){
                res[row][col] += m1[row][j]*m2[j][col];
            }
        }
    }

    printf("Result of matrix multiplication is:\n");

    for(int i=0;i<l;i++) {
        for(int j=0;j<k;j++){
            printf("%d ", res[i][j]);
        }
        printf("\n");
    }

    return 0;
}

Does anybody of you guys know what's up here?

Answer 1

Initialize the res array to 0.

int res[l][k] = {{0}};