1  
 2  #include <stdio.h>
 3  #include <stdlib.h>
 4  
 5  void greet(const char* const them)
 6  {
 7      if (them) {
 8          printf("Hello %s\n", them);
 9      } else {
10          printf("Hello world\n");
11      }
12  }
13  
14  int main(int argc, char* argv[])
15  {
16      printf("Hello, I am %s and I have %d arguments.\n", argv[0], argc);
17  
18      greet("Billy");
19      greet(0);
20  
21      return EXIT_SUCCESS;
22  }