#include <stdio.h>

void f(char s[]) {
  int i, n;
  char c;

  printf("%s:", s);

  i = 0;
  while (s[i] != '\0') {
    i++;
  }
  n = i;
  /* printf("<n = %d>", n); */
  i = 0;
  n = n - 1;
  while (i < n) {
    /* s[i] <=> s[n] */
    /* printf("(i = %d, n = %d)", i, n); */
    c = s[i];
    s[i] = s[n];
    s[n] = c;
    /* printf("[%c,%s]", c, s); */
    i++;
    n--;
  }
  printf("%s\n", s);
}

int main() {
  char a[] = "abcde";
  char b[] = "abcdef";
  char c[] = "a";
  char d[] = "";
  f(a);
  f(b);
  f(c);
  f(d);
  return 0;
}
/* end */

abcde:edcba
abcdef:fedcba
a:a
: