Contact Book Loop error

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C++

What's going is when i run it i get this error that says "main.obj : error LNK2019: unresolved external symbol "void __cdecl WriteToFile(void)" (?WriteToFile@@YAXXZ) referenced in function "void __cdecl addContact(void)" (?addContact@@YAXXZ)" and i also get one that says "C:\Users\Anikan\Documents\Visual Studio 2010\Projects\ContactBook\Debug\ContactBook.exe : fatal error LNK1120: 1 unresolved externals". If you have any advice on what i can do to fix this all help will be appreciated!

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

using namespace std;

void addContact();
void removeContact();
void editContact();
void WriteToFile();

string GetName();
string GetAdress();

int main()
{
	int yesNo;
	int ansChoice;

	do{
	cout << "Here are your choices: " << endl;
	cout << "  1. Create a Contact" << endl;
	cout << "  2. Remove a Contact" << endl;
	cout << "  3. Edit a Contact" << endl;
	cout << "  0. Exit" << endl;
	cin >> ansChoice;

	switch(ansChoice)
	{
	case 1:
		addContact();
		break;
	case 2:
		removeContact();
		break;
	case 3:
		editContact();
		break;
	case 0:
		cout << "Goodbye!" << endl;
		break;
	default:
		cout << "Goodbye!" << endl;
		break;
	}

	cout << "Do you need to do another modification?(1 for yes, 0 for no): ";
	cin >> yesNo;

	}while(yesNo);
}

void addContact()
{
	string FullName, PersonAdress;
	int getDateOfBirthYear, getDateOfBirthDay, getDateOfBirthMonth;
	long getPhoneNumber;

	FullName = GetName();
	PersonAdress = GetAdress();

	cout << "Now Enter the year " << FullName << "'s was born in: ";
	cin >> getDateOfBirthYear;
	cout << "Now the Month: ";
	cin >> getDateOfBirthMonth;
	cout << "And the Day: ";
	cin >> getDateOfBirthDay;
	cout << "\n" << "Please enter their phone number: ";
	cin >> getPhoneNumber;

	WriteToFile();
}

void WriteToFile(string FullName, string PersonAdress, int getDateOfBirthYear, int getDateOfBirthDay, int getDateOfBirthMonth, long getPhoneNumber)
{
	ofstream contactFile (FullName);
	if(contactFile.is_open())
	{
		contactFile << "Name: " << FullName << "\n";
		contactFile << "Adress: " << PersonAdress << "\n";
		contactFile << "Date of Birth: " << getDateOfBirthMonth << "/" << getDateOfBirthDay << "/" << getDateOfBirthYear << "\n";
		contactFile << "Phone Number: " << getPhoneNumber << "\n";
	}
	else{
		cout << "Error 23 Contact your Administrator :D." << endl;
	}

	//return 0;
}
void removeContact()
{

}
void editContact()
{

}
string GetName(){
	
	string FirstName, LastName, FN;

	cout << "Person's First Name: ";
	cin >> FirstName;
	cout << "Person's last Name: ";
	cin >> LastName;

	FN = FirstName + " " + LastName;

	return FN;
}
string GetAdress(){

	int adressNumber;
	string streetName, Fin;

	cout << "Please enter the name of the Street: ";
	cin >> streetName;
	cout << "Now enter the adress number: ";
	cin >> adressNumber;

	Fin = adressNumber + " " + streetName;

	return(Fin);
}