if ((system->bodies+a)->x[0] + system->x[0] < 0 || (system->bodies+a)->x[0] + system->x[0] > 640)
(system->bodies+a)->v[0] = -(system->bodies+a)->v[0];
if ((system->bodies+a)->x[1] + system->x[1] < 0 || (system->bodies+a)->x[1] + system->x[1] > 480)
(system->bodies+a)->v[1] = -(system->bodies+a)->v[1];
if ((system->bodies+a)->x[0] + system->x[0] < 0 || (system->bodies+a)->x[0] + system->x[0] > 640)
(system->bodies+a)->v[0] = -(system->bodies+a)->v[0];
if ((system->bodies+a)->x[1] + system->x[1] < 0 || (system->bodies+a)->x[1] + system->x[1] > 480)
(system->bodies+a)->v[1] = -(system->bodies+a)->v[1];