foo.cc: In function ‘bool year(int)’:
foo.cc:6:22: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    6 |         return a%4==0&&a%100!=0||a%400==0;
      |                ~~~~~~^~~~~~~~~~
foo.cc: In function ‘int monthday(int, int)’:
foo.cc:16:1: warning: control reaches end of non-void function [-Wreturn-type]
   16 | }
      | ^