/in/foo.cc: In function 'int cmp(stu, stu)':
/in/foo.cc:11:34: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  return s.sum>t.sum||s.sum==t.sum&&s.x>t.x||s.sum==t.sum&&s.x==t.x&&s.id<t.id;
                      ~~~~~~~~~~~~^~~~~~~~~
/in/foo.cc:11:67: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  return s.sum>t.sum||s.sum==t.sum&&s.x>t.x||s.sum==t.sum&&s.x==t.x&&s.id<t.id;
                                             ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~