#include 

void exchange (char *s, char *p);

main ()
{
  char *s = "hey there",
       *p = "hi there";

  printf ("%s  %s\n", s, p);
  exchange (s, p);
  printf ("%s  %s\n", s, p);
}

void exchange (char *s, char *p)
{
  char *tmp;

  tmp = s;
  s = p;
  p = tmp;
}