private void button2_Click(object sender, EventArgs e)
        {
            SqListClass L4 = new SqListClass();

            Merge3(ref L4);
            textBox4.Text = L4.DispList();
        }
        private void comboBox1_SelectedIndexChanged_1(object sender, EventArgs e)
        {
            int k = comboBox1.SelectedIndex;                  //使用combobox中的索引号来判断要执行什么操作

            if (k == 0)
            {
                textBox2.Enabled = false;
                label3.Text      = "长度";
                textBox3.Text    = L.ListLength().ToString();
            }
            else if (k == 1)
            {
                textBox2.Enabled = true;
                label3.Text      = "序号";
                label4.Text      = "元素";
                Findele();
            }
            else if (k == 2)
            {
                textBox2.Enabled = true;
                label3.Text      = "元素";
                label4.Text      = "序号";
                Findnum();
            }
            else if (k == 3)
            {
                textBox2.Enabled = true;
                label3.Text      = "序号";
                label4.Text      = "元素";
                Insert();
            }
            else if (k == 4)
            {
                textBox2.Enabled = true;
                string text3 = textBox3.Text.ToString();
                string text2 = textBox2.Text.ToString();
                label3.Text = "按序号";
                label4.Text = "按元素";
                if (text3 != "" && text2 == "")
                {
                    Deletebynum();
                }
                else if (text3 == "" && text2 != "")
                {
                    Deletebyele(text2);
                }
            }
            else if (k == 5)
            {
                textBox2.Enabled = true;
                SqListClass L1 = new SqListClass();
                SqListClass L2 = new SqListClass();
                Split(ref L1, ref L2);
                label3.Text   = "奇数序号的元素";
                label4.Text   = "偶数序号的元素";
                textBox3.Text = L1.DispList();
                textBox2.Text = L2.DispList();
            }
        }
        private void Insert()             //插入元素
        {
            int    i;
            string x, str;

            if (textBox3.Text.Trim() == "")
            {
                label2.Text = "必须输入序号";
            }
            else
            {
                try
                {
                    i = Convert.ToInt16(textBox3.Text.Trim());
                }
                catch (Exception err)
                {
                    label2.Text = "输入的序号是错误的";
                    return;
                }
                x = textBox2.Text.Trim();
                if (x == "")
                {
                    label2.Text = "操作提示:必须输入元素值";
                }
                else
                {
                    if (L.ListInsert(i, x))
                    {
                        str           = L.DispList();
                        textBox4.Text = str;
                        label2.Text   = "操作提示:成功插入元素" + x;
                    }
                    else
                    {
                        label2.Text   = "操作提示:输入的序号" + i.ToString() + "错误";
                        textBox4.Text = "";
                    }
                }
            }
        }