A Simple Calculator in Visual Basic for Beginners

Public Class Form1
    ' We create this variables as globals so they can be accessed from any where in the program.

    ' this varible is for the mathematical symbol clicked. e.g +, - .
    Dim sign As Char
    ' This variable stores the first value entered by the user.
    Dim first As Double
    ' This variable stores the second value entered by the user.
    Dim second As Double
    ' This variable stores the answer of the calculation
    Dim ans As Double
    ' This variable stores a value 1 or 0 to tell if the calculation is complete or not.
    Dim stat As Integer

    '
    Sub confirm()
        stat = 1
        first = TextBox1.Text
    End Sub
    ' This subroutine checks the mathematical symbol that was clicked using a select case statement.
    ' This is more efficient then using several if statements.
    ' Then its performs the calculation based on the symbol chosen.
    ' It then sets the calculator status to 1 to show the calculation is complete(stat=1).
    ' It then displays your result in the textbox (TextBox1.Text = ans)
    Sub action()

        Select Case sign
            Case "+"
                ans = first + TextBox1.Text
            Case "-"
                ans = first - TextBox1.Text
            Case "*"
                ans = first * TextBox1.Text
            Case "/"
                ans = first / TextBox1.Text

            Case Else

        End Select
        stat = 1
        TextBox1.Text = ans
    End Sub

    Sub addnum(ByRef a As String)

        If TextBox1.Text = 0 Then
            TextBox1.Text = a
        Else
            TextBox1.Text = TextBox1.Text & a
        End If
        If stat = 1 Then
            TextBox1.Text = a
            stat = 0
        End If
    End Sub

    ' using addnum() in the button click event prevents having to write the same code for every button click.
    ' event. The parameter in the subroutine is the number that should be added to the text button on the button click.
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        addnum(1)
    End Sub

    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
        addnum(2)
    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        addnum(3)
    End Sub

    Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
        addnum(4)
    End Sub

    Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
        addnum(5)
    End Sub

    Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
        addnum(6)
    End Sub

    Private Sub Button7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button7.Click
        addnum(7)
    End Sub

    Private Sub Button8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button8.Click
        addnum(8)
    End Sub

    Private Sub Button9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button9.Click
        addnum(9)
    End Sub

    Private Sub Button10_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button10.Click
        addnum(0)
    End Sub

    Private Sub Button_Add_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Add.Click
        sign = "+"
        confirm()
    End Sub

    Private Sub Button_Minus_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Minus.Click
        sign = "-"
        confirm()
    End Sub

    Private Sub Button_Multiply_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Multiply.Click
        sign = "*"
     confirm()
    End Sub

    Private Sub Button_Divide_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Divide.Click
        sign = "/"
       confirm()
    End Sub

    Private Sub Button1_Clear_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1_Clear.Click
        TextBox1.Text = 0
        stat = 0
        first = TextBox1.Text
    End Sub

    Private Sub Button_Equal_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Equal.Click
        action()

    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

    End Sub

    Private Sub Button_Point_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button_Point.Click
        addnum(".")
    End Sub
End Class