Restaurant Bill Calculator using Combo Box in C#

(Restaurant Bill Calculator) A restaurant wants an app that calculates a table’s bill. The app should display all the menu items from Fig. 15.53 in four ComboBoxes. Each ComboBox should contain a category of food offered by the restaurant (Beverage, Appetizer, Main Course and Dessert).

The user can choose from one of these ComboBoxes to add an item to a table’s bill. As each item is selected in the ComboBoxes, add the price of that item to the bill. The user can click the Clear Bill Button to restore the Subtotal:, Tax: and Total: fields to $0.00.

Solution:

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 Q4
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void groupBox2_Enter(object sender, EventArgs e)
        {
        }
        private void button2_Click(object sender, EventArgs e)
        {
            double total = 0;
            double subtotal = 0;
            double tax = 0;

            if (comboBox1.SelectedIndex == 0)
            {
                subtotal = subtotal + 400;
            }
            if (comboBox1.SelectedIndex == 1)
            {
                subtotal = subtotal + 50;
            }
            if (comboBox1.SelectedIndex == 2)
            {
                subtotal = subtotal + 300;
            }
            if (comboBox2.SelectedIndex == 0)
            {
                subtotal = subtotal + 400;
            }
            if (comboBox2.SelectedIndex == 1)
            {
                subtotal = subtotal + 50;
            }
            if (comboBox2.SelectedIndex == 2)
            {
                subtotal = subtotal + 300;
            }
            if (comboBox3.SelectedIndex == 0)
            {
                subtotal = subtotal + 400;
            }
            if (comboBox3.SelectedIndex == 1)
            {
                subtotal = subtotal + 50;
            }
            if (comboBox3.SelectedIndex == 2)
            {
                subtotal = subtotal + 300;
            }
            textBox7.Text = Convert.ToString(subtotal);
            tax = subtotal * 0.2;
            textBox8.Text = Convert.ToString(tax);
            total = tax + subtotal;
            textBox9.Text = Convert.ToString(total);
        }
        private void button1_Click(object sender, EventArgs e)
        {
           
        }
    }
}