Dim first As Long
Dim second As Long
Dim sign As String
Dim FirstValueEntered As Boolean


Private Sub Command1_Click(Index As Integer)
If FirstValueEntered = True Then
TextDisplay.Text = TextDisplay.Text & Command1(Index).Caption
second = Val(TextDisplay.Text)
Else
TextDisplay.Text = TextDisplay.Text & Command1(Index).Caption
first = Val(TextDisplay.Text)
End If
End Sub

Private Sub cmdPlus_Click()
If (FirstValueEntered) Then
first = first + second
TextDisplay.Text = first
second = 0
ElseIf TextDisplay.Text <> "" Then
FirstValueEntered = True
sign = cmdPlus.Caption
TextDisplay.Text = ""
End If
End Sub

Private Sub cmdMinus_Click()
If (FirstValueEntered) Then
first = first - second
TextDisplay.Text = first
second = 0
ElseIf TextDisplay.Text <> "" Then
FirstValueEntered = True
sign = cmdMinus.Caption
End If
End Sub

Private Sub cmdC_Click()
TextDisplay.Text = ""
FirstValueEntered = False
End Sub

Private Sub cmdEq_Click()
If TextDisplay.Text <> "" Then
second = Val(TextDisplay.Text)
Else
second = 0
End If
If sign = "+" Then
TextDisplay = first + second
ElseIf sign = "-" Then
TextDisplay = first - second
Else
TextDisplay = "?"
End If
FirstValueEntered = False
End Sub


I would like you to check this program.
1. if I press a number ex 1 twice it display 11
2. if I press + once it gives command for the operation it will perform
3. if I press a number ex 2 twice it display 22
4. if I press + it will display the sum of the first two number,then it gives again command for the operation it will perform,
5. if I press a number ex 1,it is appended on the number displayed, ex 33 the sum of the first two number what happened is 331.
how can I fix it.
thanks.

The fundamental problem is that you have too many program states and no way to distinguish them.

1. Nothing has been entered
2. One number has been entered and a second is being entered.
3. A second number has been entered and a third is being entered.
4. = has been pressed and there is a value on the display and the user will enter a new number.

In #2, the TextDisplay box is empty when this state starts.
In #3, the TextDisplay box is not empty when this state starts.
You need to recognize the program states and differentiate the program's operation. One idea would be to have a variable that would be set depending on the program's states (an integer). Here's another way to do it, just by adding another Boolean (it's a bit more kludgy than I would like).

Option Explicit

Dim first As Long
Dim second As Long
Dim sign As String
Dim FirstValueEntered As Boolean
Dim SecondValueEntered As Boolean

Private Sub Command1_Click(Index As Integer)
If FirstValueEntered = True Then
If SecondValueEntered Then
textDisplay.Text = Command1(Index).Caption
SecondValueEntered = False
Else
textDisplay.Text = textDisplay.Text & Command1(Index).Caption
End If
second = Val(textDisplay.Text)
Else
If SecondValueEntered Then
textDisplay.Text = Command1(Index).Caption
SecondValueEntered = False
Else
textDisplay.Text = textDisplay.Text & Command1(Index).Caption
End If
first = Val(textDisplay.Text)
End If
End Sub

Private Sub cmdPlus_Click()
If (FirstValueEntered) Then
first = first + second
textDisplay.Text = first
second = 0
SecondValueEntered = True
ElseIf textDisplay.Text <> "" Then
FirstValueEntered = True
sign = cmdPlus.Caption
textDisplay.Text = ""
End If
End Sub

Private Sub cmdMinus_Click()
If (FirstValueEntered) Then
first = first - second
textDisplay.Text = first
second = 0
ElseIf textDisplay.Text <> "" Then
FirstValueEntered = True
sign = cmdMinus.Caption
End If
End Sub

Private Sub cmdC_Click()
textDisplay.Text = ""
FirstValueEntered = False
End Sub

Private Sub cmdEq_Click()
If textDisplay.Text <> "" Then
second = Val(textDisplay.Text)
Else
second = 0
End If
If sign = "+" Then
textDisplay = first + second
ElseIf sign = "-" Then
textDisplay = first - second
Else
textDisplay = "?"
End If
FirstValueEntered = False
SecondValueEntered = True
End Sub