/in/foo.c: In function 'd':
/in/foo.c:10:6: error: 'i' undeclared (first use in this function)
  for(i=0;i<month-1;i++)
      ^
/in/foo.c:10:6: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:15:5: warning: 'main' is normally a non-static function [-Wmain]
 int main()
     ^~~~
/in/foo.c:22:1: error: expected declaration or statement at end of input
 }
 ^
/in/foo.c:8:6: warning: variable 'days' set but not used [-Wunused-but-set-variable]
  int days[]={31,y(year)?29:28,31,30,31,30,31,31,30,31,30,31};
      ^~~~
At top level:
/in/foo.c:15:5: warning: 'main' defined but not used [-Wunused-function]
 int main()
     ^~~~