What's wrong with my code, I keep getting "Undefined reference to..."?

/* main.cpp */
#include <iostream>
#include <stdexcept>
#include "PromptModule.h"
#include "ErrorHandlingModule.h" 
using namespace std;  
char GetOperator(void)
{
	char theOperator;
	cout << "Operator: ";
	cin >> theOperator;
	return theOperator;
} 
float GetOperand(void)
{
	float theOperand = 1;
	cout << "The Operand: ";
	cin >> theOperand;
	return theOperand;
}
	
float Accumulate (const char theOperator,const float theOperand)
	{
		static float myAccumulator = 0; //Inititalize to 0 when the program starts
		switch (theOperator)
		{
			case '+':
				myAccumulator = myAccumulator + theOperand;
				break; 
			case '-':
				myAccumulator = myAccumulator - theOperand;
				break;
			case '*':
				myAccumulator = myAccumulator * theOperand;
				break;
			case '/':
				myAccumulator = myAccumulator / theOperand;
				break;
			default:
				throw
					runtime_error("Error - Invalid Operator");
		};
	return myAccumulator;
	} 
int main(int argc, char* argv[])
{
	SAMSErrorHandling::Initialize();
	do
	{
		try
		{
			char Operator = GetOperator();
			float Operand = GetOperand();
			cout << Accumulate(Operator,Operand) << endl;
		}
		catch (runtime_error RuntimeError)
		{
			SAMSErrorHandling::HandleRuntimeError(RuntimeError);
		}
		catch (...)
		{
			SAMSErrorHandling::HandleNotANumberError();
		};
	}
	while (SAMSPrompt::UserWantsToContinueYOrN("More ?"));
	return 0;
}  
 
/* ErrorHandlingModule.cpp */
#include <iostream>
#include <stdexcept>
#include "ErrorHandlingModule.h" 
using namespace std; 
namespace SAMSErrorHandling
{
	using namespace std;
	
	void Inititalize(void)
	{
		cin.exceptions(cin.failbit);
	}
	
	int HandleNotAnumberError(void) //Returns error code
	{
		cerr << "Input error - not a number?" << endl;
		cin.clear();
		//Eat the bad input so we can pause the program
		char BadInput[5];
		cin >> BadInput;
		return 1; // An error occured
	}
	int HandleRuntimeError(runtime_error theRuntimeError)
		{
			cerr << theRuntimeError.what() << endl;
			return 1;
		}
}  
 
/* ErrorHandlingModule Header file */
#ifndef ErrorHandlingModuleH
#define ErrorHandlingModuleH
#include <stdexcept> 
using namespace std; 
namespace SAMSErrorHandling
{
	void Initialize(void);
	int HandleNotANumberError(void); //Returns error code
	int HandleRuntimeError(runtime_error theRuntimeError);
} 
#endif  
 
/* PromptModule.cpp */
#include <iostream>
#include "PromptModule.h" 
using namespace std; 
namespace SAMSPrompt
{  
bool UserWantstoContinueYOrN (const char *theThingWeAreDoing)
	{
		char DoneCharacter;
		bool InvalidCharacterWasEntered = false;
		do
		{
			cout << endl << theThingWeAreDoing << " - Press \'n\' and \'Enter\' to stop: ";
			cin >> DoneCharacter; 
			InvalidCharacterWasEntered = 
			!
			(
				(DoneCharacter == 'y')
				||
				(DoneCharacter == 'n')
			); 
				if (InvalidCharacterWasEntered)
					{
						cout << "...Error - " << "please enter \"y\" or \"n\"."<<endl;
					};
		}while (InvalidCharacterWasEntered);
	return (DoneCharacter != 'n'); 
	}
}  
 

/* PromptModule header */
#ifndef PromptModuleH
#define PromptModuleH  
namespace SAMSPrompt
{
bool UserWantsToContinueYOrN (const char *theThingWeAreDoing);
}
#endif