foo.cc: In function ‘bool leap(int)’:
foo.cc:6:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    6 |         if(y%4==0&&y%100!=0||y%400==0) return true;
      |            ~~~~~~^~~~~~~~~~
foo.cc: In function ‘int monthday(int, int)’:
foo.cc:14:14: error: ‘day’ was not declared in this scope
   14 |         else day=31;
      |              ^~~
foo.cc: In function ‘int main()’:
foo.cc:37:35: error: expected ‘;’ before ‘m’
   37 |                 day-=monthday(y,m)
      |                                   ^
      |                                   ;
   38 |                 m++;
      |                 ~