/in/foo.c: In function 'main':
/in/foo.c:6:2: error: too few arguments to function 'fgets'
  fgets(a);
  ^~~~~
In file included from /in/foo.c:1:0:
/usr/include/stdio.h:624:14: note: declared here
 extern char *fgets (char *__restrict __s, int __n, FILE *__restrict __stream)
              ^~~~~