类中的私有指针在方法中更改时不会更新

我有这些类（为了可读性而剥离）

class node {
   public:
   int x;
   node* next;
   node(){}
   ~node(){}
 };
 class intLinkedList{
     public:
         intLinkedList();
         ~intLinkedList();
         void Add (int newX);
     private:
         node* root;
  };

这是Add中的实现

void intLinkedList::Add (int newX){
  node* newNode = new node();
  newNode->x = newX;
  newNode->next = NULL;
  std::cout << "nn" << root << "nn" << std::flush;
  if (root == NULL){
    root = newNode;    
    return;
  }
  node * current;
  current = root;
  while (current->next != NULL){
    current = current->next;
  }
  current->next = newNode;
  return;
}

当我在设置后立即打印出根指向的地址时，它会显示一个有效的地址。但是，下次调用Add时，root再次变为NULL。我无法想象是什么行为导致了这种情况。这在其他地方是绝对不用的。

我完全意识到我缺少一些简单的东西。如果你因为问题很简单而倾向于否决投票，那就去别处吧。这个平台的目的是让程序员在我们有编码头脑时能够团结起来互相帮助。

编辑：这是驱动程序。

#include <string>
#include <iostream>
#include "intLinkedList.h"
using namespace std;
void AddValue(intLinkedList MyList);
void GetValue(intLinkedList MyList);
void InsertValue(intLinkedList MyList);
void DeleteValue(intLinkedList MyList);
void PrintList(intLinkedList MyList);
int main(){
    intLinkedList MyList;
    int Option;
    while (true){
        cout << "nnMain Menun---------nn1) Add Valuen2) See Valuen3)     Insert Value at Positionn4) Delete Value at Positionn5) Print Listn6)     Exitnn";
    cin >> Option;
        switch (Option){
            case 1: AddValue(MyList); break;
            case 2: GetValue(MyList); break;
            case 3: InsertValue(MyList); break;
            case 4: DeleteValue(MyList); break;
            case 5: PrintList(MyList); break;
            case 6: exit(0);
        }
    }
}
void AddValue(intLinkedList MyList){
    int NewValue;
    cout << "What value should be added?n";
    cin >> NewValue;
    MyList.Add(NewValue);
}
void GetValue(intLinkedList MyList){
    int Position;
    cout << "What position do you want the value of?n";
    cin >> Position;
    MyList.Get(Position);
}
void InsertValue(intLinkedList MyList){
    int Position;
    int NewValue;
    cout << "What position do you wnat to insert after?n";
    cin >> Position;
    cout << "nWhat value do you want to insert?n";
    cin >> NewValue;
    MyList.Insert(NewValue, Position);
}
void DeleteValue(intLinkedList MyList){
    int Position;
    cout << "What position do you want to delete?n";
    cin >> Position;
    MyList.Delete(Position);
}
void PrintList(intLinkedList MyList){
    cout << MyList.Print();
}