gistfile1.c

#include <stdio.h>

int main(int argc, char* argv[])
{
  char* i = 0;
  char* str = "Hello, World";

  for(i = str + 11; i >= str; i--)
      putchar((char)*i);

  return 0;
}

gistfile2.c

#include <stdio.h>

int main(int argc, char* argv[])
{
  if(argc <= 1)
    return 1;

  char* i = 0;
  char* str = argv[1];

  for(i = str + strlen(str); i >= str; i--)
      putchar((char)*i);

  return 0;
}

int
strlen(char *str)
{
  int i;
  for (i = 0; str[i] != '\0'; ++i) {}
  return i;
}