这个程序的错误提示是

错误 1 未能找到类型或命名空间名称“SaveEmail”(是否缺少 using 指令或程序集引用?) G:\C#实验\第七章\实例7-5\实例7-5\Form1.cs 24 13 实例7-5

能不能看一下应该怎么改？

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;


namespace 实例7_5
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }


        private void btnCheakEmail_Click(object sender, EventArgs e)
        {
            SaveEmail saveEmail = new SaveEmail();
            try
            {
                if (saveEmail.CheckEmail(txtEmail.Text))
                {
                    lblShow.Text = "检查成功";
                }
            }
            catch(EmailErrorException ex)
            {
                lblShow.Text = ex.Message;
            }
        }
    }
    public class EmailErrorException : ApplicationException
    {
        public EmailErrorException() { }
        public EmailErrorException(string message) : base(message) { }
        public EmailErrorException(string message, System.Exception innerException) : base(message, innerException) { }
        public override string Message
        {
            get
            {
                return "Email格式不正确：" + base.Message;
            }
        }
        public class SaveEmail
        {
            public bool CheackEmail(string email)
            {
                string[] strSign = email.Split('@');
                if (strSign.Length != 2 || strSign[0].Length == 0 || strSign[1].Length == 0)
                {
                    throw new EmailErrorException("@符号不正确！");
                }
                else
                {
                    int index = strSign[1].IndexOf('.');
                    if (index <= 0 || index >= strSign[1].Length - 1)
                    {
                        throw new EmailErrorException(".符号不正确");
                    }
                }
                return true;
            }
        }

    }
}