/in/foo.cc: In function 'int gbs(int, int)':
/in/foo.cc:10:9: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return res;
         ^~~
/in/foo.cc: In function 'int gys(int, int)':
/in/foo.cc:20:9: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return res;
         ^~~
/in/foo.cc: In function 'int main()':
/in/foo.cc:26:18: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<gbs(a,b)<<" "<<gys(a,b)<<endl;
                  ^~~
/in/foo.cc:26:30: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<gbs(a,b)<<" "<<gys(a,b)<<endl;
                              ^