/in/foo.cc: In member function 'int Datetime::day()':
/in/foo.cc:22:30: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   22 |                 if(nian%4==0 && nian%100!=0||nian%400==0)
      |                    ~~~~~~~~~~^~~~~~~~~~~~~~
/in/foo.cc:21:15: warning: suggest explicit braces to avoid ambiguous 'else' [-Wdangling-else]
   21 |             if(yue==2)
      |               ^
/in/foo.cc:26:9: warning: control reaches end of non-void function [-Wreturn-type]
   26 |         }
      |         ^