/in/foo.cc: In function 'int weishu(int)':
/in/foo.cc:22:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:49:11: warning: 'res' may be used uninitialized in this function [-Wmaybe-uninitialized]
  cout<<res;
           ^