未将对象引用实例化为对象实例？？？？？求解脱。。

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

namespace ConsoleApplication5
{
class BSTree
{

   public class node 

{
public int key;
public sbyte data;
public node lchild;
public node rchild;
}

internal static class DefineConstantsBSTree
{
public const int MaxSize = 100;
}
public static class GlobalMembersBSTree
{
public static int[] path = new int[DefineConstantsBSTree.MaxSize];
public static void DispBST(node bt)

{
    if (bt!=null)
    {
        Console.Write("{0:D}",bt.key);
        if (bt.lchild!=null || bt.rchild!=null)
        {
            Console.Write("(");
            DispBST(bt.lchild);
            if (bt.rchild!=null)
                Console.Write(",");
            DispBST(bt.rchild);
            Console.Write(")");
        }
    }
}
public static int InsertBST(ref node p, int k) 
{

    if (p == null) 
    {

        p.key = k;
        p.lchild = p.rchild = null;
        return 1;
    }
    else if (k == p.key)
        return 0;
    else if (k<p.key)
        return InsertBST(ref p.lchild, k); 
    else
        return InsertBST(ref p.rchild, k);
}
public static node CreatBST(int[] A, int n)

{
    node bt = null; 
    int i = 0;
    while (i<n)
        InsertBST(ref bt, A[i++]); 
    return bt; 
}


public static int SearchBST(node bt, int k, int[] path, int i)
{
    if (bt == null)
        return i;
    else if (k == bt.key) 
    {
        path[i+1] =bt.key; 
        return i+1;
    }
    else
    {
        path[i+1] =bt.key;
        if (k<bt.key)
            return SearchBST(bt.lchild, k, path, i+1); 
        else
            return SearchBST(bt.rchild, k, path, i+1); 
    }
}


public static void SearchResult(node bt, int k1)
{
    int r;
    int j;
    r = SearchBST(bt, k1, path, -1);
    for (j = 0; j<=r; j++)
        Console.Write("{0,3:D}",path[j]);
    Console.Write("\n");
}

internal static int Main()
{
    node bt;

    int k1 = 65;
    int k2 = 32;
    int[] a = {43,91,10,18,82,65,33,59,27,73};
    int n = 10;
    Console.Write("创建的BST树:");
    bt = CreatBST(a, n);
    DispBST(bt);
    Console.Write("\n");
    Console.Write("  查找{0:D}关键字:",k1);
    SearchResult(bt, k1);
    Console.Write("  查找{0:D}关键字:",k2);
    SearchResult(bt, k2);
    return 0;
}








    }
}

}

CreatBST(int[] A, int n)的方法里

 while (i<n)
        InsertBST(ref bt, A[i++]); 

数组下标越界了，这样改一下

 while (i<n)
        InsertBST(ref bt, A[++i]); 

你不是逗么，if(n==NULL){n.k}不错才见鬼呢，如果为NULL的时候n=new test()

p这个对象都为null了，你怎么还能使用它调用成员呢

(╯з╰)不好意思我回答错了，看岔了，确实是p == null的问题

应该是p!=null吧，哪里抄的程序。。。。。。。。。。。。。。