public void ShowGrade()
        {
            try
            {
                Console.WriteLine("请输入要插入年级号：");
                string gradeNo = Console.ReadLine();
                Console.WriteLine("请输入要插入名称：");
                string gradename = Console.ReadLine();
                int reed = dbo.InsertGrade(gradename, gradeNo);
                if (reed == -1)
                {
                    Console.WriteLine("数据库操作出现异常!");
                }
                else
                {
                    Console.WriteLine("插入成功！\n年级号：{0}年级名称：{1}", gradeNo, gradename);
                    Console.WriteLine("是否继续增加年级记录？\n输入Y继续，输入N退出并返回菜单");
                    char ch = Console.ReadKey().KeyChar;
                    try
                    {
                        Console.WriteLine(Convert.ToInt32(ch));
                        return;
                    if(Convert.ToInt32(ch)==78)
                    {
                        ShowMenu();
                    }
                    else if (Convert.ToInt32(ch) == 89)
                    {
                        ShowGrade();
                    }
                    else
                    {
                        Console.WriteLine("请输入Y或N！");
                    }
                    }
                    catch
                    {
                        Console.WriteLine("异常");
                    }
                }
            }
            catch
            {
                Console.WriteLine("插入失败！");
            }
        }



为什么调用别的功能以后还显示 Y或N
为什么输入键盘上的任意键他都返回菜单

为什么调用别的功能以后还显示 Y或N
就你贴出来的代码没有反映出这个问题

为什么输入键盘上的任意键他都返回菜单
Console.WriteLine(Convert.ToInt32(ch));
return;
写个return做什么,你显示出输入的字符以后,就return了,后面代码当然不执行了