foo.cc: In function ‘bool y(int)’:
foo.cc:5:18: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    5 |         if(n%4==0&&n%100!=0||n%400==0)return true;
      |            ~~~~~~^~~~~~~~~~
foo.cc: In function ‘int monthday(int, int)’:
foo.cc:11:26: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
   11 |                 if(a%4==0&&a%100!=0||a%400==0)return 29;
      |                    ~~~~~~^~~~~~~~~~