Matrix Multiplication

[vishublc]

I have implemented matrix mulitplier function and storing the result in one of them,but giving wrong result
plzz tell me where i am wrong..

void multiply(long long int F[4][4],long long int M[4][4]) {
long long int s1,s2,s3,s4;
int x,y,k,i,j;
int Z[4][4];
for(i=0;i<4;i++)
{
    s1 = 0;
s2 = 0;
s3 = 0;
s4 = 0;
for(k=0;k<4;k++) 
    {
//printf(" y is %d",y);             
s1+=(F[i][k] * M[k][0]);

    s2+=(F[i][k] * M[k][1]);

    s3+=(F[i][k] * M[k][2]);

    s4+=(F[i][k] * M[k][3]);

     }

    F[i][0] = s1;
F[i][1] = s2;
F[i][2] = s3;
F[i][3] = s4;
   }
}