/in/foo.c: In function 'leapyear':
/in/foo.c:6:16: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
  if (year%4==0 && year%100!=0 || year%400==0)
      ~~~~~~~~~~^~~~~~~~~~~~~~
/in/foo.c: In function 'main':
/in/foo.c:32:17: warning: unused variable 'i' [-Wunused-variable]
  int year,month,i,sum=0;
                 ^
/in/foo.c: In function 'mon':
/in/foo.c:28:9: warning: 'm' may be used uninitialized in this function [-Wmaybe-uninitialized]
  return m;
         ^
/in/foo.c: In function 'main':
/in/foo.c:37:2: warning: 'm' may be used uninitialized in this function [-Wmaybe-uninitialized]
  printf("%d\n",sum);
  ^~~~~~~~~~~~~~~~~~