Is this program efficient - vb.net

Question

I've put together a small calculator application that works quite well, but despite being a novice to VB.net I know that the program probably isn't as efficient as it should be. The idea is that upon inputting numbers into a textbox and pressing a mathematical operator, the textbox will reset and continue the equation, storing the past values entered.
Dim input1 As Double
Dim numfunction As Double
'numerical functions (null = 0, add = 1, subtract = 2, divide = 3, multiply = 4)
Private Sub btnAdd_Click(sender As Object, e As RoutedEventArgs) Handles btnAdd.Click
If txtNum.Text = "" Then
MsgBox("Please enter a number")
Else
numfunction = 1
input1 = input1 + txtNum.Text
txtNum.Text = ""
End If
End Sub
Private Sub btnEqual_Click(sender As Object, e As RoutedEventArgs) Handles btnEqual.Click
If txtNum.Text = "" Then
MsgBox("Please enter a final number")
End If
If numfunction = 1 Then
txtNum.Text = txtNum.Text + input1
input1 = 0
End If
End Sub
Could you point me in the right direction as to what I should replace add or remove to make my programs more efficient in the future? Keep in mind that the BtnAdd_Click event is just one of 4 (add, sub, divide, multiply) and because of that btnEqual_Click will have a few if statements, checking for what function the user has put in, and if there is anything in txtNum at all.
Thanks in advance, I'm not asking for anyone to complete my code, but I'd love to see what options I have so I make more efficient programs in the future.

Answer 1

With a little initial effort you could simplify this task by using the power of object oriented programming:
Public Class Form1
' hold a reference to all operations in a list of operations
Private _operations As New List(Of Operation)
' the operation currently choosen
Private Property _currentOperation As Operation
' the 2 numbers you want to perform the operations on
Private _number1 As Double = 0
Private _number2 As Double = 0
Public Sub New()
InitializeComponent()
SetupOperations()
TextBox1.Text = 0
End Sub
Public Sub ChangeOperation(operation As Operation)
_number1 = _currentOperation.FunctionDelegate.Invoke(_number1, _number2)
TextBox1.Text = _number1
_currentOperation = operation
End Sub
Private Sub SetupOperations()
_operations.Add(New Operation(Me, btnAdd, Function(x, y)
Return x + y
End Function))
' heres the crux ... you use anonymous method to define your functions hook them to the form (Me) and the related Button
' all at once
' Similar for the other operations (subtract / multiply / divide / pow, and so on)
Dim equalsOperation As New Operation(Me, btnEqual, Function(x, y)
Return y
End Function)
_operations.Add(equalsOperation)
_currentOperation = equalsOperation
End Sub
' for this example i used only one textbox and a lable indicating wheter the number entered is a valid double
Private Sub TextBox1_TextChanged(sender As Object, e As EventArgs) Handles TextBox1.TextChanged
Dim result As Double
If Double.TryParse(TextBox1.Text, result) Then
_number2 = result
lblValid.Text = "Valid" ' tell the user that the number entered is valid or not
Else
lblValid.Text = "Invalid"
End If
End Sub
''' <summary>
''' An Operation that hooks up a button click and can execute the operation
''' </summary>
Public Class Operation
Private _owningForm As Form1
Public Property FunctionDelegate As Func(Of Double, Double, Double) ' use a delegate to a Func that returns double with 2 double parameters
Public Sub New(owningForm As Form1, boundButton As Button, functionDelegate As Func(Of Double, Double, Double))
Me.FunctionDelegate = functionDelegate
Me._owningForm = owningForm
AddHandler boundButton.Click, AddressOf boundButton_Click ' make the operation hook up on the click event
End Sub
Private Sub boundButton_Click()
_owningForm.ChangeOperation(Me)
End Sub
End Class
End Class
Hope this is not too confusing for you, I intended to show you a bigger world than simple routines and tons of eventhandlers

Answer 2

You could simplify your code by inserting your checking code into a separate subroutine.
Sub CheckVals()
If txtNum.Text = "" Then
MsgBox("Please enter a final number")
End If
If numfunction = 1 Then
txtNum.Text = txtNum.Text + input1
input1 = 0
End If
End Sub
You would then reference this sub from your two button click events.
Private Sub btnAdd_Click(sender As Object, e As RoutedEventArgs) Handles btnAdd.Click
CheckVals()
End Sub