Visual Basic 6.0 Source Code for Simple Calculator

This guide provides the complete Visual Basic 6.0 source code for a simple calculator application. The code includes all necessary components for basic arithmetic operations, user interface elements, and event handling. Whether you're learning VB6 or need a reference for your own projects, this implementation demonstrates fundamental programming concepts in a practical way.

Introduction

Visual Basic 6.0 (VB6) remains an important legacy language for many developers, particularly in enterprise environments where it was widely used. While newer languages have largely replaced VB6, understanding its fundamentals can still be valuable for maintaining older systems or learning the principles of event-driven programming.

This simple calculator demonstrates core VB6 concepts including form design, event handling, and basic arithmetic operations. The implementation is straightforward enough to serve as a learning tool while being functional enough for practical use.

Visual Basic 6.0 Source Code

The following is the complete source code for a simple calculator in Visual Basic 6.0. This implementation includes all necessary components for basic arithmetic operations.

Calculator Form Code

' Calculator Form Code
' frmCalculator.frm

VERSION 5.00
Begin VB.Form frmCalculator
   Caption         =   "Simple Calculator"
   ClientHeight    =   3000
   ClientLeft      =   45
   ClientTop       =   315
   ClientWidth    =   4500
   LinkTopic       =   "Form1"
   ScaleHeight     =   3000
   ScaleWidth      =   4500
   StartUpPosition =   1  'Windows Default
   Begin VB.TextBox txtDisplay
      Height          =   315
      Left            =   480
      TabIndex        =   0
      Text            =   "0"
      Top             =   360
      Width           =   3540
   End
   Begin VB.CommandButton cmd1
      Caption         =   "1"
      Height          =   315
      Left            =   480
      TabIndex        =   1
      Top             =   720
      Width           =   855
   End
   Begin VB.CommandButton cmd2
      Caption         =   "2"
      Height          =   315
      Left            =   1365
      TabIndex        =   2
      Top             =   720
      Width           =   855
   End
   Begin VB.CommandButton cmd3
      Caption         =   "3"
      Height          =   315
      Left            =   2250
      TabIndex        =   3
      Top             =   720
      Width           =   855
   End
   Begin VB.CommandButton cmdPlus
      Caption         =   "+"
      Height          =   315
      Left            =   3135
      TabIndex        =   4
      Top             =   720
      Width           =   855
   End
   Begin VB.CommandButton cmd4
      Caption         =   "4"
      Height          =   315
      Left            =   480
      TabIndex        =   5
      Top             =   1080
      Width           =   855
   End
   Begin VB.CommandButton cmd5
      Caption         =   "5"
      Height          =   315
      Left            =   1365
      TabIndex        =   6
      Top             =   1080
      Width           =   855
   End
   Begin VB.CommandButton cmd6
      Caption         =   "6"
      Height          =   315
      Left            =   2250
      TabIndex        =   7
      Top             =   1080
      Width           =   855
   End
   Begin VB.CommandButton cmdMinus
      Caption         =   "-"
      Height          =   315
      Left            =   3135
      TabIndex        =   8
      Top             =   1080
      Width           =   855
   End
   Begin VB.CommandButton cmd7
      Caption         =   "7"
      Height          =   315
      Left            =   480
      TabIndex        =   9
      Top             =   1440
      Width           =   855
   End
   Begin VB.CommandButton cmd8
      Caption         =   "8"
      Height          =   315
      Left            =   1365
      TabIndex        =   10
      Top             =   1440
      Width           =   855
   End
   Begin VB.CommandButton cmd9
      Caption         =   "9"
      Height          =   315
      Left            =   2250
      TabIndex        =   11
      Top             =   1440
      Width           =   855
   End
   Begin VB.CommandButton cmdMultiply
      Caption         =   "*"
      Height          =   315
      Left            =   3135
      TabIndex        =   12
      Top             =   1440
      Width           =   855
   End
   Begin VB.CommandButton cmd0
      Caption         =   "0"
      Height          =   315
      Left            =   480
      TabIndex        =   13
      Top             =   1800
      Width           =   855
   End
   Begin VB.CommandButton cmdDecimal
      Caption         =   "."
      Height          =   315
      Left            =   1365
      TabIndex        =   14
      Top             =   1800
      Width           =   855
   End
   Begin VB.CommandButton cmdEquals
      Caption         =   "="
      Height          =   315
      Left            =   2250
      TabIndex        =   15
      Top             =   1800
      Width           =   855
   End
   Begin VB.CommandButton cmdDivide
      Caption         =   "/"
      Height          =   315
      Left            =   3135
      TabIndex        =   16
      Top             =   1800
      Width           =   855
   End
   Begin VB.CommandButton cmdClear
      Caption         =   "C"
      Height          =   315
      Left            =   480
      TabIndex        =   17
      Top             =   2160
      Width           =   3540
   End
End
Attribute VB_Name = "frmCalculator"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False

Calculator Module Code

' Calculator Module Code
' frmCalculator.bas

Option Explicit

Private currentValue As Double
Private previousValue As Double
Private currentOperation As String
Private isNewNumber As Boolean

Private Sub cmd0_Click()
    AddDigit "0"
End Sub

Private Sub cmd1_Click()
    AddDigit "1"
End Sub

Private Sub cmd2_Click()
    AddDigit "2"
End Sub

Private Sub cmd3_Click()
    AddDigit "3"
End Sub

Private Sub cmd4_Click()
    AddDigit "4"
End Sub

Private Sub cmd5_Click()
    AddDigit "5"
End Sub

Private Sub cmd6_Click()
    AddDigit "6"
End Sub

Private Sub cmd7_Click()
    AddDigit "7"
End Sub

Private Sub cmd8_Click()
    AddDigit "8"
End Sub

Private Sub cmd9_Click()
    AddDigit "9"
End Sub

Private Sub cmdDecimal_Click()
    If isNewNumber Then
        txtDisplay.Text = "0."
        isNewNumber = False
    ElseIf InStr(txtDisplay.Text, ".") = 0 Then
        txtDisplay.Text = txtDisplay.Text & "."
    End If
End Sub

Private Sub cmdClear_Click()
    currentValue = 0
    previousValue = 0
    currentOperation = ""
    txtDisplay.Text = "0"
    isNewNumber = True
End Sub

Private Sub cmdPlus_Click()
    SetOperation "+"
End Sub

Private Sub cmdMinus_Click()
    SetOperation "-"
End Sub

Private Sub cmdMultiply_Click()
    SetOperation "*"
End Sub

Private Sub cmdDivide_Click()
    SetOperation "/"
End Sub

Private Sub cmdEquals_Click()
    If currentOperation <> "" Then
        previousValue = Val(txtDisplay.Text)
        Select Case currentOperation
            Case "+"
                currentValue = currentValue + previousValue
            Case "-"
                currentValue = currentValue - previousValue
            Case "*"
                currentValue = currentValue * previousValue
            Case "/"
                If previousValue <> 0 Then
                    currentValue = currentValue / previousValue
                Else
                    MsgBox "Cannot divide by zero", vbExclamation
                    Exit Sub
                End If
        End Select
        txtDisplay.Text = CStr(currentValue)
        currentOperation = ""
        isNewNumber = True
    End If
End Sub

Private Sub AddDigit(digit As String)
    If isNewNumber Then
        txtDisplay.Text = digit
        isNewNumber = False
    Else
        If txtDisplay.Text = "0" Then
            txtDisplay.Text = digit
        Else
            txtDisplay.Text = txtDisplay.Text & digit
        End If
    End If
End Sub

Private Sub SetOperation(operation As String)
    If currentOperation <> "" Then
        cmdEquals_Click
    End If
    currentValue = Val(txtDisplay.Text)
    currentOperation = operation
    isNewNumber = True
End Sub

How the Calculator Works

The calculator implements basic arithmetic operations using event-driven programming. Here's how it works:

User Interface

The form contains:

A display text box (txtDisplay) to show the current number and results
Number buttons (0-9) for input
Operation buttons (+, -, *, /) for calculations
Decimal point button for floating-point numbers
Equals button to compute the result
Clear button to reset the calculator

Event Handling

Each button has a corresponding Click event handler that performs specific actions:

Number buttons append digits to the current number
Operation buttons store the current number and prepare for the next operation
The equals button performs the calculation and displays the result
The clear button resets all values and the display

Calculation Logic

The module maintains several private variables:

currentValue - stores the first operand or accumulated result
previousValue - stores the second operand
currentOperation - stores the pending operation (+, -, *, /)
isNewNumber - flag to indicate if a new number should start

The calculation follows this sequence:

User enters first number and selects an operation
The calculator stores the number and operation
User enters second number and clicks equals
The calculator performs the operation and displays the result

Note: This implementation handles basic arithmetic but doesn't include error checking for invalid operations or overflow conditions.

Example Calculation

Let's walk through a sample calculation: 25 + 17 = 42

User clicks "2" then "5" - display shows "25"
User clicks "+" - calculator stores 25 as currentValue and "+" as currentOperation
User clicks "1" then "7" - display shows "17"
User clicks "=" - calculator computes 25 + 17 = 42 and displays "42"

This demonstrates the basic flow of the calculator's operation handling.

Frequently Asked Questions

Can I modify this calculator to include more operations?: Yes, you can add more operations by creating additional buttons and corresponding event handlers. The current structure makes it easy to extend with new functions.
How do I change the appearance of the calculator?: You can modify the form properties in the VB6 IDE to change colors, sizes, and positions of controls. The current design uses standard VB6 controls.
What happens if I divide by zero?: The calculator includes a check for division by zero and displays an error message. This prevents the application from crashing.
Can I save the calculator as an executable?: Yes, you can compile the project in VB6 to create an executable file (.exe) that can be run on any Windows system with the VB6 runtime installed.
Is this code compatible with modern Windows versions?: The code should work on modern Windows versions as long as the VB6 runtime is installed. However, for new projects, consider using more modern development tools.