/in/foo.cc: In function 'int main()':
/in/foo.cc:8:2: error: expected ';' before 'cout'
  cout<<month<<"月"<<31<<endl;
  ^~~~
/in/foo.cc:9:16: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if (year%4==0 && year%100!=0 || year%400==0)
      ~~~~~~~~~~^~~~~~~~~~~~~~
/in/foo.cc:10:9: error: 'mouth' was not declared in this scope
   cout<<mouth<<"月"<<29<<endl;
         ^~~~~