Need help! replaceing part of an null character array with a string

[mgckb10]

I got everything to work besides the replacing nouns function, which should switch out the words listed, if listed in the array with a random noun from a text file. I get no errors when compiling, but after the greeting function, the program is stuck and I have to force it to quit. What's wrong with the code in the replace nouns function

main.cpp

#include "moefables_function.h"
#include <iostream>
#include <fstream>
#include <ctime>
#include <cstdlib>
#include <cstring>
#include <string>
using namespace std;

int main()
{
  string nouns, nouns2, tale, tale2;
  char answer;
  Greeting();
  do
  {
    tale = fable();
    nouns = Nouns1();
    nouns2 = Nouns2();
    cout << tale;
    tale2 = replaceNouns(tale, nouns, nouns2);
    cout << tale2 << endl;
    MoeRant();
    Moral();
    cout << "\nDo you wish to hear another fable? (y/n)" << endl;
    cin >> answer;
  }while(answer == 'y' || answer == 'Y');
  cout << "\nThank you for listening, come back again.";
  return 0;
}

function.h

#ifndef MOEFABLES_FUNCTION_H
#define MOEFABLES_FUNCTION_H

#include <iostream>
#include <fstream>
#include <ctime>
#include <cstdlib>
using namespace std;

//Outputs a message
//Pre: none
//Post: outputs a message on the screen
void Greeting();

//gets the fable as a string
//Pre: none
//Post: brings back the value or string
string fable();

//25% chance to get a rant outputted
//Pre: none
//Post: outputs a rant on the screen at times
void MoeRant();

//gets a noun from a list
//Pre: none
//Post: returns the string
string Nouns1();

//gets a noun from a list
//Pre: none
//Post: returns the string
string Nouns2();

//get a random moral message outputted
//Pre: none
//Post: outputs a moral on the screen
void Moral();

//switches two nouns with two words throughout the fable
//Pre: need to have a value for the two nouns and fable
//Post: returns the new value for fable
string replaceNouns(string fable, const string noun, const string noun2);

#endif 

function.cpp

#include "moefables_function.h"
#include <iostream>
#include <fstream>
#include <ctime>
#include <cstdlib>
#include <cstring>
#include <string>
using namespace std;

void Greeting()
{
  cout << "Welcome to Moe's Fable creater" << endl;
  return;
}

string fable()
{
  ifstream fableFilein;
  int randNum;
  string fable;
  srand(time(NULL));
  randNum = rand() % 5;
  if(randNum == 0)
  {
    fableFilein.open("fable1.txt");
    getline(fableFilein,fable);//takes the words of text file and makes it a   string
    fableFilein.close();
  }
  else if(randNum == 1)
  {
    fableFilein.open("fable2.txt");
    getline(fableFilein,fable);
    fableFilein.close();
  }
  else if(randNum == 2)
  {
    fableFilein.open("fable3.txt");
    getline(fableFilein,fable);
    fableFilein.close();
  }
  else if(randNum == 3)
  {
    fableFilein.open("fable4.txt");
    getline(fableFilein,fable);
    fableFilein.close();
  }
  else if(randNum == 4)
  {
    fableFilein.open("fable5.txt");
 getline(fableFilein,fable);
    fableFilein.close();
  }
  return fable;
}

void MoeRant()
{
  int randNum2, a;
  string rant;
  ifstream rantsFilein;
  srand(time(NULL));
  randNum2 = rand() % 4;
  a = rand() % 6;
  if(randNum2 == 0)
  {
    rantsFilein.open("Moe-rants.txt");
    do
    {
      getline(rantsFilein, rant);
    }while(--a >= 0);//gets a random line from text file
    rantsFilein.close();//ends the stream for that certain text file
    cout << " " << rant << endl;
}
  else
  {
    cout << " ";
  }
  return;
}


string Nouns1()
{
  int a;
  string nouns;
  ifstream finNouns;
  srand(time(NULL));
  finNouns.open("list1.txt");
  a = rand() % 14;
  do
  {
    getline(finNouns,nouns);
  }while(--a >= 0);

  finNouns.close();
  return nouns;
}

string Nouns2()
{
  int a;
  string noun;
  ifstream finNoun;
  srand(time(NULL));
  finNoun.open("list2.txt");
  a = static_cast<int>(rand() % 24);
  do
  {
    getline(finNoun,noun);
  }while(--a >= 0);

  finNoun.close();
  return noun;
}

void Moral()
{
  ifstream finMoral;
  string moral;
  int a;
  srand(time(NULL));
  a = (rand() % 6) + 1;
  cout << "\nThe Moe-rale of this story is: ";
  finMoral.open("Moe-rals.txt");
  do
  {
    getline(finMoral, moral);
  }while(--a >= 0);
  finMoral.close();
  cout << moral << endl;
  return;
}

string replaceNouns(string fable, string noun, string noun2)
{
  int i = 0;
  fable.c_str();
  noun.c_str();
  noun2.c_str();
  while(&fable[i] != '\0')
  {
   if(strcpy(&fable[i],"boy") == 0 || strcpy(&fable[i],"ant") == 0 || strcpy(&fable[i],"fox") == 0 || strcpy(&fable[i],"man") == 0 || strcpy(&fable[i],"milkmaid") == 0)
    {
      fable[i] = noun[i];
    }
    else if(strcpy(&fable[i],"serpant") == 0 ||strcpy(&fable[i],"grasshopper")  == 0 || strcpy(&fable[i],"goat") == 0 || strcpy(&fable[i],"trees") ==0 ||strcpy(&fable[i],"milkpail") == 0)
    {
      fable[i] = noun2[i];
    }

  }
  return fable;
}

[coder777]

you cannot use strcpy() with std::string.
use the string function replace() instead. See:

http://www.cplusplus.com/reference/string/string/replace/

Why do you use strcpy() in an if clause? Maybe you want to find the strings within fable? See:

http://www.cplusplus.com/reference/string/string/find/