foo.c: In function ‘main’:
foo.c:12:34: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
   12 |                 else if(year%4==0&&year%100!=0||year%400==0)
      |                         ~~~~~~~~~^~~~~~~~~~~~~
foo.c:13:17: error: expected expression before ‘else’
   13 |                 else
      |                 ^~~~