```
int C[10][20];
int * mmatrix (int A[ 10 ][ 5 ], int B[ 5 ][ 20 ])
{
int i, j, k;
for(i = 0; i < 10; ++i)
for(j = 0; j < 20; ++j) {
for(k = 0; k < 5; ++k)
C[ i ][ j ] += A[ i ][ k ] * B[ k ][ j ];
}
return C;
}
```

Why can not my compiler convert to this? What is the problem over here?

Thanks