Simple calculator in C# (fixing for a friend)

calc.cs

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
 
namespace testlaiwinform
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
 
        private void textBox1_TextChanged(object sender, EventArgs e)
        {  
        }
 
        private void textBox3_TextChanged(object sender, EventArgs e)
        {
        }
 
        private void textBox2_TextChanged(object sender, EventArgs e)
        {

        }
        
        private void button1_Click(object sender, EventArgs e)
        {
            int bien1;
            int bien2;
            int kq;
            
            bien1 = int.Parse(textBox1.Text);
            bien2 = int.Parse(textBox3.Text);
            
            if (textBox2.Text == "+") {
                kq = bien1 + bien2;
            } else if (textBox2.Text == "-"){
                 kq = bien1 - bien2;
            } else if (textBox2.Text == "x"){
                kq = bien1 * bien2;
            } else if (textBox2.Text == ":"){
                kq = bien1 / bien2;
            }   
            
            string kq1;
            kq1 = kq.ToString();
            label2.Text = kq1;
        }
    }
}