#include <stdio.h>
void exchange(char *s, char *t) {
  char *p, *q;
  for (p = s, q = t; *p != '\0' && *q != '\0'; p++, q++) {
    char t;
    t = *p;
    *p = *q;
    *q = t;
  }
}

int main(void){
  char string1[] = "abcdefg";
  char string2[] = "hijklmn";

  printf("string1 = %s string2 = %s\n", string1, string2);
  printf("exchange(string1, string2)\n");
  exchange(string1, string2);
  printf("string1 = %s string2 = %s\n", string1, string2);
  return 0;
}
/* end */

string1 = abcdefg string2 = hijklmn
exchange(string1, string2)
string1 = hijklmn string2 = abcdefg