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)
      |            ~~~~~~^~~~~~~~~~
foo.cc: In function ‘int monthday(int, int)’:
foo.cc:23:16: warning: ‘d’ may be used uninitialized [-Wmaybe-uninitialized]
   23 |         return d;
      |                ^
foo.cc:12:13: note: ‘d’ was declared here
   12 |         int d;
      |             ^