/in/ex4.c:4:6: warning: return type of 'main' is not 'int' [-Wmain]
 void main() {
      ^~~~
/in/ex4.c: In function 'main':
/in/ex4.c:5:23: error: expected expression before 'time_t'
     time_t   dt   =   time_t now;
                       ^~~~~~
/in/ex4.c:6:25: error: request for member 'ToString' in something not a structure or union
     char*   str   =   dt.ToString( "yyyy-MM-dd   HH:mm:ss ");
                         ^
/in/ex4.c:6:13: warning: unused variable 'str' [-Wunused-variable]
     char*   str   =   dt.ToString( "yyyy-MM-dd   HH:mm:ss ");
             ^~~
/in/ex4.c:5:14: warning: variable 'dt' set but not used [-Wunused-but-set-variable]
     time_t   dt   =   time_t now;
              ^~