/in/foo.cc: In function 'int main()':
/in/foo.cc:12:26: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %lf",&n,&r);
                          ^
/in/foo.cc:13:29: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%lf %lf",&x0,&y0);
                             ^
/in/foo.cc:24:31: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%lf %lf",&x,&y);
                               ^