WF累加求和5

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

private void button1_Click(object sender, EventArgs e)
{
string str1 = textBox1.Text;
string str2 = textBox2.Text;
int m1, m2;
if (int.TryParse(str1, out m1) == false)
{
MessageBox.Show("数字1格式错误");
return;

}
if (!int.TryParse(str2, out m2))
{
MessageBox.Show("数字2格式错误");
return;
}
if(m1>=m2)
{
MessageBox.Show("第二个数要大于第一个数，请重新输入");
return;
}
int sum=0;
for( int n =m1;n<=m2;n++)
{
sum= sum+n;

}
textBox3.Text = Convert.ToString(sum);
}
}
}