#define X_SIZE 60
#define Y_SIZE 30

int matrix[X_SIZE][Y_SIZE];

void init_matrix(void)
{
    int x,y;    /* current element to zero */

    for (x = 0; x < X_SIZE; x++) {
        for (y = 0; y < Y_SIZE; y++) {
            matrix[x][y] = -1;
        }
    }
}