The "deep story" of the source code begins when the user clicks the "Total" button. This is Event-Driven Programming
Private Sub CalculateTotal() Dim subTotal As Decimal = 0 For Each row As DataGridViewRow In dgvCart.Rows subTotal += Convert.ToDecimal(row.Cells("Total").Value) Next
Below is a comprehensive guide and a modular breakdown of the source code for a standard Desktop Billing Application. 1. Project Prerequisites
discountAmt = subtotal * (Convert.ToDecimal(txtDiscountPercent.Text) / 100) grandTotal = subtotal - discountAmt + totalTax
Imports System.Data.SqlClient Public Class dbConfig Public conn As New SqlConnection("Data Source=YOUR_SERVER;Initial Catalog=BillingDB;Integrated Security=True") Public Sub OpenConnection() If conn.State = ConnectionState.Closed Then conn.Open() End Sub Public Sub CloseConnection() If conn.State = ConnectionState.Open Then conn.Close() End Sub End Class Use code with caution. 4. Designing the Billing UI Your main form ( frmBilling.vb ) should include: Product ID, Quantity, Price, Customer Name. DataGridView: To display the current items in the cart. Buttons: "Add to Cart", "Generate Invoice", "Clear". 5. Core Logic: Adding Items to Grid