C# WinApp สอบถามวิธีใช้งาน unsafe ครับ พอผมก๊อบโค้ดมาวางก็ ขึ้น Error โดยที่ยังไม่ได้เขียนอะไรเพิ่มเลย

Store "DO FORM frmXXX" TO fpdPointer
&fpdPointer //มันทำงาน === frm.Show() นั่นแหละ
//นี่ก็คือ Pointer

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace Unsafe
{
    class Program
    {
        unsafe static void Main(string[] args)
        {
            int[] x = new int[10]; // x.Length = 10 All Value = 0
            unsafe {
                int* p1, p2, p3; // OK
                //int *p1, *p2, *p3 ;  Invalid in C#
                int a;
                int* b;
                //int c, *b; Invalid in C#
                a = 25;
                b = &a;
                

                int i = 7;
                // Unsafe method: uses address-of operator (&):
                SquarePtrParam(&i);

                Console.WriteLine("b = {0}", *b);//returns b = 25
                Console.WriteLine("i = {0}", i); //returns i = 49
                Console.ReadLine();
            }
        }

        // Unsafe method: takes pointer to int: 
        unsafe static void SquarePtrParam(int* p)
        {
            *p *= *p;
        }

        static void test()
        {
            String a = "Hello World";
            String b = a;
            a = "Hello";
            Console.WriteLine("{0}, {1}", a, b); // Hello, Hello World
            Console.WriteLine(a == b); //false
            Console.WriteLine(object.ReferenceEquals(a, b)); //false
        }

    }
}

protected static void NotImplemented() {
            ExternalException e = new ExternalException(SR.GetString(SR.UnsafeNativeMethodsNotImplemented), NativeMethods.E_NOTIMPL);
            throw e;
        }