Использование необъявленного идентификатора ‘FunctionName’ C ++ Xcode

Все, что я пытаюсь сделать, это вызвать простую функцию из другой функции, почему я получаю ошибки при каждом вызове addRomanDigit в функции convert_to_Roman? Программа не завершена, я просто пытаюсь завершить первую функцию.

//
//  RomanCalculator.cpp
//  HelloWorld
//
//  Created by Feroze on 6/13/13.
//  Copyright (c) 2013 Feroze Shahpurwala. All rights reserved.
//

#include <iostream>
#include <iomanip>
#include <string>
#include <fstream>

using namespace std;string convert_to_Roman(int value)
{
string retVal;
/* if (value < 0)
{
retVal ="-";
value = -value;
} */

retVal = addRomanDigit(retVal, value/1000, 'M'); // ERROR HERE and for one below 'Use of undeclared identifier 'addRomanDigit'
value = value % 1000;
retVal = addRomanDigit(retVal, value/500,  'D');
value = value % 500;
retVal = addRomanDigit(retVal, value/100,  'C');
value = value % 100;
retVal = addRomanDigit(retVal, value/50,   'L');
value = value % 50;
retVal = addRomanDigit(retVal, value/10,   'X');
value = value % 10;
retVal = addRomanDigit(retVal, value/5,    'V');
value = value % 5;
retVal = addRomanDigit(retVal, value,      'I');

return retVal;
}string addRomanDigit(string starting, int num, char digit)
{
string retval = starting;
for (int i=0; i < num; i++)
retval += digit;
return retval;
}int convert_from_Roman(int x)
{
return 0;
}

int calc_romans(/*figure out the calling sequence*/)
{
// fill in your code
// We will be discussing the string class in more detail in
// subsequent chapters.  The following snippet illustrates a few
// features we will encounter :

// string str = "abcdefg";
// for (int i=0; i < str.length(); i++)
// {
//     char c = str[i];  // pull of characters one at a time from the string
// }

}void print_Result(/* figure out the calling sequence */)
{
// fill in your code
}

// Note the call by reference parameters:
void get_Data(ifstream & infile, string & operand1, string & operand2, char & oper, bool & badInput)
{
// Read in operand1, operand2, oper
// Check to see if an error condition has occurred.
// Set badInput for any error, but main will only print out an error condition
// if the reason for the error is something other than
// hitting an end of file(out of data) condition.

//
}

// I would rather have you leave main alone and just make your function calls above match
// the calling sequence required by main below:

int main()
{
ifstream infile;
infile.open("roman.txt");
if (!infile)
{
cout << "Can't open roman.txt" << endl;
return -1;
}

while(!infile.eof())
{
string operand1, operand2;
char oper;
bool badInput;
get_Data(infile, operand1, operand2, oper,  badInput);

if (badInput)
{
if (!infile.eof()) // Check to see if we are the end of the file
cout << "Skipping Bad input"<<endl;  // Must be a bad input
}
else
{
int value1 = convert_from_Roman(operand1);
int value2 = convert_from_Roman(operand2);
cout << "The first operand is " << operand1 <<
"(" << value1 << ")"<<endl;
cout << "The second operand is " << operand2 <<
"(" << value2 << ")"<<endl;
cout <<"The operator is " << oper << endl;
int answer = calc_romans(value1, value2, oper);
print_Result(operand1, operand2, convert_to_Roman(answer), answer);
cout << endl;
}
}

}