#include <string.h>

void reverse(char* str)
{
  int length = strlen(str);
  char temp;
  int j = length - 1;

  for (int i = 0; i < j; ++i)
  {
     temp = str[i];
     str[i] = str[j];
     str[j] = temp;
     --j;
  }
}

int main(int argc, char* argv[])
{
   char str[] = "Hello";
   reverse(&str[0]);
   printf("%s\n", str);
   return 0;
}