Wanting to Make Nested For Loop

#include <stdio.h>
  3 #include <stdlib.h>
  4
  5 int main(void)
  6 {
  7     char letter[6] = { 'A','B','C','D','E','F' };
  8
  9     printf("%c\n", letter[5]);
 10     printf("%c%c\n", letter[5], letter[4]);
 11     printf("%c%c%c\n", letter[5], letter[4], letter[3]);
 12     printf("%c%c%c%c\n", letter[5], letter[4], letter[3], letter[2]);
 13     printf("%c%c%c%c%c\n", letter[5], letter[4], letter[3], letter[2],
 14             letter[1]);
 15     printf("%c%c%c%c%c%c\n", letter[5], letter[4], letter[3], letter[2],
 16             letter[1], letter[0]);
 17     return 0;
 18 }