C# Girilen Sayıya Kadar Olan Sayılardan Asal Olanları Bulan Program

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();
        }
        double  sayı, i = 1,a;
        private void button1_Click(object sender, EventArgs e)
        {
            if (textBox1.Text != "")
            {
                listBox1.Items.Clear();
                sayı= double.Parse(textBox1.Text);
                for (i = 2; i <= sayı; i ++)
                {
                    bool asal = true;
                    for ( a = 2; a < i; a++)
                    {
                        if (i % a == 0)
                        {
                            asal = false;
                          
                        }
                    }
                    if (asal)
                    {
                        listBox1.Items.Add(i);
                    }
                }
            }
            else
            {
                MessageBox.Show("Değer aralığı giriniz !");
            }
        }
        }
        }