C# metni tamsayıya çevirmede hata.

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 WindowsFormsApplication1
{
    public partial class Form1 : Form
    
    public Form1()
    {
        InitializeComponent();
    }
    
    private void Form1_Load(object sender, EventArgs e)
    {
        int sayi1, sayi2;
    
    private void button1_Click(object sender, EventArgs e)
    {
    int toplam = sayi1 + sayi2;
    
    int tahmin = int.Parse(textBox1.Text);
    
    if (tahmin == toplam)
       label5.Text = "Tebrikler, Sonuç Doğru..";
    else
       label5.Text = "Hatalı Sonuç.";
    }
    
    private void button2_Click(object sender, EventArgs e)
    {
		Random rastgeleSayi = new Random();
		sayi1 = rastgeleSayi.Next(0, 100);
		sayi2 = rastgeleSayi.Next(0, 100);
		label3.Text = sayi1.ToString();
		label4.Text = sayi2.ToString();
    }
}