foo.c: In function ‘main’:
foo.c:9:23: warning: suggest parentheses around ‘&&’ within ‘||’ [-Wparentheses]
    9 |         if (year%4==0 && year%100!=0 || year%400==0)
      |             ~~~~~~~~~~^~~~~~~~~~~~~~
foo.c:6:9: warning: unused variable ‘arr’ [-Wunused-variable]
    6 |     int arr[12]={31,28,31,30,31,30,31,31,30,31,30,31};
      |         ^~~