Sumar en C Sharp 2008, error no definido

[maycolalvarez]

eso es VB no C#:

this.TextBox3.Text= (Convert.ToInt32(this.TextBox1.Text) + Convert.ToInt32(this.TextBox2.Text)).ToString();

Código C#:

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 sumas
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void button1_Click(object sender, EventArgs e)
        {
            this.textBox3.Text = (Convert.ToInt32(this.textBox1.Text) + Convert.ToInt32(this.textBox2.Text)).ToString();
        }
    }
}