foo.c: In function ‘ct’:
foo.c:2:5: warning: type of ‘year’ defaults to ‘int’ [-Wimplicit-int]
    2 | int ct(year,month)
      |     ^~
foo.c:2:5: warning: type of ‘month’ defaults to ‘int’ [-Wimplicit-int]
foo.c:6:35: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    6 |                 if (year % 4 == 0 && year % 100 != 0 || year % 400 == 0)//判断是否为闰年
      |                     ~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
foo.c:26:1: warning: control reaches end of non-void function [-Wreturn-type]
   26 | }
      | ^