#include <string.h>
#include <stdio.h>

void replace_char(char str[], int n, char c)
{
  str[n] = c;
}

int main (void)
{  
  char* string = "Hello World!";

  printf ("%s\n", string);
  replace_char(string, 10, 'a');
  printf ("%s\n", string);

  string = strdup("Hello World!");

  printf ("%s\n", string);
  replace_char(string, 10, 'a');
  printf ("%s\n", string);

  return 0;
}