Invoice Bill

Design

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 Item_Qty_Rate_Total
{
    public partial class Form1 : Form
    {
        int r; // Row index variable

        public Form1()
        {
            InitializeComponent();
            r = 0; // Initialize row index
        }

        private void button1_Click(object sender, EventArgs e)
        {
            // Adding a new row to DataGridView
            dataGridView1.Rows.Add();

            // Assign values from TextBoxes to DataGridView cells
            dataGridView1[0, r].Value = textBox1.Text; // Item Name
            dataGridView1[1, r].Value = textBox2.Text; // Quantity
            dataGridView1[2, r].Value = textBox3.Text; // Rate

            // Calculate Total (Quantity * Rate)
            textBox4.Text = (Convert.ToDouble(textBox3.Text) * Convert.ToDouble(textBox2.Text)).ToString();

            // Assign total to DataGridView
            dataGridView1[3, r].Value = textBox4.Text;
            
            // Move to next row index
            r++;
        }
    }
}

Output