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;

namespace 累加
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            string s1 = textBox1.Text;
            string s2 = textBox2.Text;
            int i1, i2;
            if (int.TryParse(s1, out i1) == false)
            {
                MessageBox.Show("输入的第一个数是不合法的！");
                return;
            }
            if (int.TryParse(s2, out i2) == false)
            {
                MessageBox .Show ("输出的第二个数是不合法的！");
                return;
            }
            if (i1 >= i2)
            {
                MessageBox.Show("第一个数不能大于或等于第二个数！！！");
                return;
            }
            int sum = 0;
            for (int i = i1; i <= i2; i++)
            {
                sum = sum + i;
            }
            textBox3.Text = Convert.ToString(sum);
           
        }
    }
}