>734
if(!r) {
  r = 4119;
  r = a*(r%c)-d*(r/c);
}
        ↓
if(!r) r = 4119;
r = a*(r%c)-d*(r/c);

x = myrand()/(RAND_MAX+1.0);
y = myrand()/(RAND_MAX+1.0);
        ↓
x = myrand();
y = myrand();