Question about the What's In the Box code game assignment - pass-by-reference

Question

I am struggling to understand how to properly use pass by value and reference in this program. It keeps saying identifier is undefined when I put the Int in the main function. But when it's out of the main function it works fine. I can't use it outside of the main function otherwise it's an automatic 0. Am I just missing code that identifies it?
I didn't explain the program very well. It's essentially the Monty Hall problem but with boxes. The user then tries to guess the right box. The biggest issue I had was getting the non prize box to appear to the user in the output.
I am very new to coding so I am probably overlooking something.
#include <stdlib.h>
#include <iomanip>
#include <iostream>
#include <time.h>
#include <string>
using namespace std;
/*******************************************************************************
* Function Name: main()
* Parameters: None
* Return Value: int
* Purpose: To execute the main function of the program. Performs loops and takes user input to execute the game.
*****************************************************************************/
void BoxCheck(int);
void PrizeBox(int&);
//int UserGuess = 0;
int main()
{
int UserChoice;
int UserGuess;
int BoxReveal;
int PrizeB;
// int Prize;
//char Switch;
cout << "Wellcome to Pandora's Prize!" << endl;
cout << "Infront of you there are three doors, and behind one of them is the grand prize!" << endl;
cout << "But in the the other two they contain a stink bomb." << endl;
cout << "It's your job to guess which one has the prize behind it." << endl;
cout << "Door 1?" << endl;
cout << "Door 2?" << endl;
cout << "Door 3?" << endl;
PrizeBox(PrizeB);
cin >> UserGuess;
BoxReveal != (PrizeB || UserGuess);
// cout << "The host revealed box number " << BoxReveal << " ." << endl;
//if (true)
//{
if (UserGuess == 1)
{
cout << "You picked box 1." << endl;
cout << "The host revealed box number " << BoxReveal << " ." << endl;
cout << "Would you like to stay with box number 1 or switch." << endl;
//cin >> UserChoice;
}
else if (UserGuess == 2)
{
cout << "You picked box 2." << endl;
cout << "The host revealed box number " << BoxReveal << " ." << endl;
cout << "Would you like to stay with box number 2 or switch." << endl;
//cin >> UserChoice;
}
else if (UserGuess == 3)
{
cout << "You picked box 3." << endl;
cout << "The host revealed box number " << BoxReveal << " ." << endl;
cout << "It contains a red snapper!" << endl;
cout << "Would you like to stay with box number 3 or switch." << endl;
//cin >> UserChoice;
}
else
{
cout << "This isn't a number associated with a box. Try again." << endl;
}
//}
/* if (true)
{
} */
//PrizeBox(Prize);
if (UserChoice == UserGuess)
{
cout << "You chose to stay with your original box." << endl;
BoxCheck(UserGuess);
}
else if (UserChoice != UserGuess) //|| UserChoice != BoxReveal)
{
cout << "You decided to switch." << endl;
BoxCheck(UserGuess);
}
/*else if (UserChoice != UserGuess || BoxReveal)
{
cout << "You decided to switch." << endl;
BoxCheck(UserGuess);
} */
else
{
cout << "Your answer was out of the parameters." << endl;
BoxCheck(UserGuess);
}
//BoxCheck(UserGuess);
system("pause");
return 0;
}
void PrizeBox(int& PrizeB)
{
srand(time(NULL));
PrizeB = rand() % 3 + 1;
//Prize = rand() % 3 + 1;
//cin >> PrizeB;
/* BoxReveal = !(PrizeBox || boxChoice);
cout << "Here is one of the box's opened! " << boxReveal << " ." << endl;
BSwitch = (boxChoice || boxReveal); */
}
void BoxCheck(int UserChoice)
{
if (UserChoice == PrizeB)
{
cout << "WOW YOU WON!!!!" << endl;
}
else if (UserChoice != PrizeB)
{
cout << "Sorry you got a red snapper" << endl;
}
else
{
cout << "Sorry you got a red snapper" << endl;
}
}