Undeclared Identifier in class that is declared private?

[Arc]

Hey guys I have a class called validID. its broken up into validID.h and validID.cpp.

In validID.h I declare int id as private.

and in validID.cpp I try to set a value to id, but I get a compile error saying it is undeclared....

Here is my code, can you see what I'm doing wrong?

Thanks!

//validID.h

#ifndef VALIDID_H
#define VALIDID_H

class validID {


public:
    validID(int = 0);  //default constructor


    int getID() const; //return ID number
    void setID(int);   //set ID number


private:
    int id; //id number

}; //end class validID

#endif

//-----------------------------------------------------------------

//validID.cpp

#include <iostream>

using std::cin;
using std::cout;
using std::endl;

#include "validID.h"

#include "errorHandler.h"



validID::validID(int idNum)
{
    
}// end constructor


void setID(int idNum)
{

if(idNum < 1 || idNum > 10000)
    {
        throw errorHandler();

    }else{ 

       id = idNum; //here is where the error is coming from

    }// end if

}// end setID