基类变量的值如何从派生类的变量中延迟

在C#程序中，基类的值低于派生类的源，该变量是继承的，基类是抽象的，但变量仅在基类中声明。这是 C# 控制台程序

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace TestApplication
{
    class MainClass
    {
        abstract class CBaseClass
        {
            public int iCount;
            public CBaseClass()
            {
                Console.WriteLine("CBaseClass created");
                iCount = 30;
            }
            public virtual void Add() { iCount += 20; }
            public virtual void Add(int iAdd) { iCount += iAdd; }
            public void Subtract() { iCount -= 20; }
            public abstract void Subtract(int iSubtract);
            public override string ToString()
            {
                return base.ToString() + ".. Method of BaseClass";
            }
            ~CBaseClass() { Console.WriteLine("CBaseClass deleted"); }
        };
        class CDerivedClass : CBaseClass 
        {
            public CDerivedClass() 
            { 
                Console.WriteLine(" CDerivedClass created.");
                iCount = 50;
            }
            public override void Add()
            {
                iCount += 20;
            }
            public void Add(int iAdd)
            { 
            iCount  += iAdd;
            }
            public void Subtract() 
            {
                iCount -= 40;
            }
            public sealed override void Subtract(int iSubtract)
            {
                iCount -= 10;
            }
            ~CDerivedClass() { Console.WriteLine("CDerivedClass deleted 'n"); }
      };

        static void Main(string[] args)
        {
            CDerivedClass deriveObject = new CDerivedClass();
            CBaseClass basePointer = new CDerivedClass();
            CDerivedClass notUsed;
            Console.WriteLine("1:" + deriveObject.iCount);
            deriveObject.Add();
            Console.WriteLine("2:" + deriveObject.iCount);
            basePointer.Add(30);
            Console.WriteLine("3:" + basePointer.iCount);
            basePointer.Subtract();
            Console.WriteLine("4:" + basePointer.iCount);
            basePointer.Subtract(20);
            Console.WriteLine("5:" + basePointer.iCount);
            Console.WriteLine("6:{0}",basePointer);
            Console.ReadLine();
        }
    }
}

这是输出：

CBaseClass created
CDerivedClass created.
CBaseClass created
CDerivedClass created.
1:50
2:70
3:80
4:60
5:50
6:TestApplication.MainClass+CDerivedClass..Method of BaseClass

在上面的输出中，我无法理解..当我们调用基类方法add(30)时。

basePointer.Add(30); 当我们调用此方法时...在该值之前，iCount值为 70。但在此之后，它变成了 50。如何？我期望输出3：100

CDerivedClass deriveObject = new CDerivedClass();
CBaseClass basePointer = new CDerivedClass();
CDerivedClass notUsed;
// deriveObject.iCount == 50
// basePointer.iCount == 50

Console.WriteLine("1:" + deriveObject.iCount); // 1:50
deriveObject.Add();
// CDerivedClass.Add is called on deriveObject
// deriveObject.iCount == 70
Console.WriteLine("2:" + deriveObject.iCount); // 2:70
basePointer.Add(30);
// CDerivedClass.Add is called on basePointer
// basePointer.iCount == 80
Console.WriteLine("3:" + basePointer.iCount); // 3:80
basePointer.Subtract();
// CBaseClass.Subtract is called on basePointer, since `CDerivedClass` does not
// override the Subtract method.
// basePointer.iCount == 60
Console.WriteLine("4:" + basePointer.iCount); // 4:60
basePointer.Subtract(20);
// CDerivedClass.Subtract is called on basePointer. *Note* that this subtracts 10.
// basePointer.iCount == 50
Console.WriteLine("5:" + basePointer.iCount); // 5:50
Console.WriteLine("6:{0}",basePointer);
Console.ReadLine();