/in/foo.c: In function 'main':
/in/foo.c:5:9: warning: zero-length gnu_printf format string [-Wformat-zero-length]
  printf("");
         ^~
/in/foo.c:11:17: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
   else if(a%4==0&&a%100!=0||a%400==0)
           ~~~~~~^~~~~~~~~~