перегрузка операторов

#include <iostream>
#include <cstdio>
using namespace std;
class mString{
 
  char *str;
  int len;
public:
  mString();
 
  mString(const char *word);
 
  mString(const mString &word);
 
  ~mString();
 
  void print() const;
 
  mString operator + (const mString op2);
 
  mString operator * (const int n);
 
  mString operator = (const mString op2);
 
  char &operator [] (const int pos);
 
  friend mString operator * (int n, const mString op);
 
  friend ostream &operator << (ostream &stream, const mString word);
};

#include <iostream>
#include <cstdio>
#include "mString.h"
#include "func.h"
using namespace std;
 
 
int main(){
    char s[20] = "abcde";
    mString word1(s);
    mString word2 = "flower";
    mString word3 = "three";
 
    cout << (word1 + word2 = word3) << endl ;
}

mString mString::operator + (const mString op){
  mString tmp(*this);
 
  tmp.strcat(op.str);
 
  return tmp;
}
 
mString mString::operator * (const int n){
  mString tmp;
 
  if (n <= 0){
    cout << "wrong number\n" ;
    return *this;
  }
 
  if (!str) return *this;
 
  for (int i = 0; i < n ; i++){
    tmp.strcat(str);
  }
  len = len * n;
  tmp.str[len] = '\0';
 
  return tmp;
}
 
 
mString mString::operator = (const mString op){
    if (str) delete []str;
 
    len = op.len;
    if (len){
      str = new char [len + 1];
      strcpy(str,op.str) ;
      str[len] = '\0';
    }
    else str = 0;
    return *this;
}
 
char& mString::operator [] (int pos){
  return str[pos - 1];
}
 
ostream &operator << (ostream &stream, const mString word){
  if (!word.empty()){
    stream << word.str ;
  }
  else stream << "Empty string\n";
  return stream;
}
 
mString operator * (int n, const mString op){
  if (n <= 0){
    cout << "wrong number\n" ;
    return op;
  }
  mString tmp;
 
  for (int i = 0; i < n ; i++){
    tmp.strcat(op.str);
  }
  tmp.len = op.len * n;
 
  return tmp;
}

const mString mString::operator + (const mString op){
  mString tmp(*this);
 
  tmp.strcat(op.str);
 
  return tmp;
}

std::string w1, w2, w3;
std::cout << (w1 + w2 = w3); //ok

string && str = w1 + w2;
str += "ok";