foo.cc: In function ‘int monthday(int, int)’:
foo.cc:7:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    7 |         if(y%4==0&&y%100==0||y%400==0)
      |            ~~~~~~^~~~~~~~~~
foo.cc: In function ‘int main()’:
foo.cc:19:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
   19 |         if(y%4==0&&y%100==0||y%400==0)
      |            ~~~~~~^~~~~~~~~~