c# windowsform

Because of school I should use do windows for c# programming, next week first midterm! an example of this week ->

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 csharpForm
{
    public partial class frmMain : Form
    {
        public frmMain()
        {
            InitializeComponent();
        }

        private void btnEnter_Click(object sender, EventArgs e)
        {
            
            switch(int.Parse(txtSayi.Text))
            {
                case 1:
                    txtColor.BackColor=System.Drawing.Color.Red;
                    break;
                case 2:
                    txtColor.BackColor=System.Drawing.Color.Yellow;
                    break;
                case 3:
                    txtColor.BackColor=System.Drawing.Color.Blue;
                    break;
                case 4:
                    txtColor.BackColor = System.Drawing.Color.BlueViolet;
                    break;
                case 5:
                    txtColor.BackColor = System.Drawing.Color.Brown;
                    break;
                case 6:
                    txtColor.BackColor = System.Drawing.Color.CadetBlue;
                    break;
                case 7:
                    txtColor.BackColor = System.Drawing.Color.CornflowerBlue;
                    break;
                case 8:
                    txtColor.BackColor = System.Drawing.Color.DarkMagenta;
                    break;
                case 9:
                    txtColor.BackColor = System.Drawing.Color.Black;
                    break;
                case 10:
                    txtColor.BackColor = System.Drawing.Color.Green;
                    break;
                default:
                    MessageBox.Show("sayi [1,10] araliginda olmali!");
                    break;
            }


            
        }

        private void btnHesapla_Click(object sender, EventArgs e)
        {

            MessageBox.Show("Sonuc:" + int.Parse(txtSayi1.Text)*int.Parse(txtSayi2.Text));
        }

        private void btnAy_Click(object sender, EventArgs e)
        {
            for (int i = 0; i < int.Parse(txtAy.Text); i++)
            {
                txtSonuc.Text = txtSonuc.Text + (int.Parse(txtUcret.Text) * (i + 1)).ToString() + Environment.NewLine;
            }
        }


    }
}

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