delta_x 70 usr/sample/balls/balls.c int delta_x, delta_y; delta_x 78 usr/sample/balls/balls.c delta_x = (random() % 10) + 1; delta_x 95 usr/sample/balls/balls.c x += delta_x; delta_x 98 usr/sample/balls/balls.c delta_x = -delta_x;