const int X_SIZE = 60;
const int Y_SIZE = 30;

int matrix[X_SIZE][Y_SIZE];

void init_matrix(void)
{
    register int index;		// element counter 
    register int *matrix_ptr;	// Current element

    matrix_ptr = &matrix[0][0];
    for (index = 0; index < X_SIZE * Y_SIZE; ++index) {
	*matrix_ptr = -1;
	++matrix_ptr;
    }
}