Employee Salary calculator windows project in C#

Below is the window project in c# which calculates the net salary of the employee. It takes employee id, name and designation as input and calculates the salary according to the designation of the employee. The project has static data. I have not implemented a database for storing data. in future will share projects who will have database to store data. Thanks for visiting my blog. I will try to make this blog is best source of learning for you.    

Below is the design view of the project:

Below is the source code of the project:

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 Employee_Salary_calculator_demo
{
    public partial class Form1 : Form
    {
        int empno;
        String name;
        float basic, ta, da, hra, spa, pt, pf, ppf, ins, atotal, dtotal, netsal;

       
        private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedIndex == 0)
            {

         
                textBox4.Text = "" + 30000;
                spa = 15000;
                ins = 8000;
                textBox11.Text = spa.ToString();
                textBox12.Text = ins.ToString();

            }
            if (comboBox1.SelectedIndex == 1)
            {

             textBox4.Text = "" + 20000;
                spa = 10000;
                ins = 5000;
                textBox11.Text = spa.ToString();
                textBox12.Text = ins.ToString();
            }
            if (comboBox1.SelectedIndex == 2)
            {

         
                textBox4.Text = "" + 10000;
                spa = 5000;
                ins = 1500;
                textBox11.Text = spa.ToString();
                textBox12.Text = ins.ToString();
            }
        }

        String desig;
        public Form1()
        {
            InitializeComponent();
        }

     
        private void button1_Click(object sender, EventArgs e)
        {
            //empno = Int32.Parse(textBox1.Text);
           // name = textBox2.Text;
            desig = comboBox1.SelectedText;
            if (desig == "Manager") {
                basic = 15000;
            }
            else if (desig == "Supervisor")
                basic = 10000;
            else if (desig == "Worker")
                basic = 7000;
            basic = Int32.Parse(textBox4.Text);
            ta = (basic * 14) / 100;
            da = (basic * 12) / 100;
            hra = (basic * 15) / 100;
            pt = (basic * 5) / 100;
            pf = (basic * 8) / 100;
            ppf = (basic * 10) / 100;
            textBox5.Text = ta.ToString();
            textBox6.Text = pt.ToString();
            textBox7.Text = da.ToString();
            textBox8.Text = pf.ToString();
            textBox9.Text = hra.ToString();
            textBox10.Text = ppf.ToString();
            textBox11.Text = spa.ToString();
          //  spa = Int32.Parse(textBox11.Text);

            atotal = ta + da + hra + spa;
            dtotal = pt + pf + ppf + ins;
            netsal = basic + atotal - dtotal;
            textBox13.Text = atotal.ToString();
            textBox14.Text = dtotal.ToString();
            textBox15.Text = netsal.ToString();
        }
    }
}