error : pointer being freed not allocated

I have typed this code from a book after learning about classes/objects in c++.
It runs until the user enters name for player 1, but then the error
"Conquest game classes objects(491) malloc: *** error for object 0x100007280: pointer being freed was not allocated
*** set a breakpoint in malloc_error_break to debug"

I dont see any pointers used in this code, nor any memory allocated with "new"(which are both covered in the next chapter of the book).

Is there a problem with the code from the book, or have I made a silly mistake. I have tried going over the code looking for typing errors, but can't see any, also I tried to solve the malloc / pointer not freed problem with google searches but couldn't see how this code used them.

Code:

#include <iostream>
#include <string>
using namespace std;

//handles each nation for each player
class Nation{
public:
	int land;
	int troops;
private:
	string name;
	int food;
	int gold;
	int people;
	int farmers;
	int merchants;
	int blacksmiths;
public:
	Nation (string lName);
	Nation();
	~Nation();
	bool takeTurn();
private:
	void menu(void);
};

Nation nation1;
Nation nation2;

//sets the default nation values
Nation::Nation(string lName):
	name(lName),land(20), food(50), troops(15), gold(100), people(100),
farmers(0), merchants(0), blacksmiths(0){}

//a default constructor
Nation::Nation(){}

//takes a turn for player
bool Nation::takeTurn(){
	cout<<"It's now" <<name<< "'s turn.\n";
	people += land * 0.2;
	food += farmers - people * 0.25;
	gold += merchants * 20;
	troops += blacksmiths;
	menu();
	if (nation1.land <= 0 || nation2.land<=0) {
		return false;
	}//if
	return true;
}//bool nation

void Nation::menu(){
	while (true) {
		int input = 0;
		cout << "Food " << food<< "\nGold"<<gold
		<<"\nland "<<land<<"\nMerchants "<< merchants<<"\nTroops "
		<<troops<<"\nUnemployed "<< people<<"\n";
		cout<<"1) Buy Land.\n"
			<<"2) Hire Farmers\n"
			<<"3) Hire merchants\n"
			<<"4) Hire Weaponsmiths\n"
			<<"5) Attack!\n"
			<<"6)Take Turn\n";
		cin>>input;
		switch (input) {
			case 1://buys land
				cout << "You buy "<<gold/20<<" sections of land\n";
				land += gold/20;
				gold %=20;
				cout<< "You now have "<<gold<< "gold\n";
				
				break;
				
				case 2:
				farmers += people;
				cout<<"you hired " << people<< " farmers\n";
				people = 0;
					break;
				
				case 3:
				merchants += people;
				cout<< "You hired " << people<< "merchants\n";
				people = 0;
					break;
				
				case 4:
				blacksmiths += people;
				cout<< "You hired " << people<< "blacksmiths\n";
				people = 0;
				break;
					
				case 5:
					cout<< "the war wages into the night and all die\n";
				if (nation1.troops < nation2.troops) {
					nation2.land += 10;
					nation1.land -= 10;
				}//if
				
				else if (nation1.troops > nation2.troops){
					nation2.land -= 10;
					nation1.land += 10;
				}//else if
				
				nation1.troops = 0;
				nation2.troops = 0;
				break;
				
				case 6:
				return; //ends the turn
					break;


		}//while
		
	}//switch
}//menu






int main(){
	string tempString;
	cout<<"Welcome to the conquest\n";
	cout<<"What is your name player 1?\n";
	cin>>tempString;
	nation1 = Nation(tempString);
	
	
	cout<<"What is your name player 2?\n";
	cin>>tempString;
	nation2 = Nation(tempString);
	while (nation1.takeTurn() && nation2.takeTurn()) {
		
	}
	return 0;
}//main

Which OS/Compiler are you using?

Apart from adding

Code:

Nation::~Nation(){}

it seems find to me.

Code:

$ g++ --version
g++ (Ubuntu 4.3.3-5ubuntu4) 4.3.3
Copyright (C) 2008 Free Software Foundation, Inc.
This is free software; see the source for copying conditions.  There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

I am using Xcode

I uncommented the destructor declearation in the class Nation

Code:

~Nation();

and added a destructor definition

Code:

//a default constructor
Nation::Nation(){}
Nation::~Nation(){}

compiled and ran it but got the same error after the first name input.

If it cannot reach the message "What is your name player 2?" then there is most likely something you left out when posting this, as neither takeTuen, nor menu will be getting called and what's left we can determine to be fine simply by examination.
As confirmation, we know that you at least left out the destructor definition.
Thus the bug is probably in the code you left out. Or perhaps this is not successfully compiling when you make a change and is just re-running a previous build that had errors.