Visual Basic - Calculator II coding dilemmas - vb.net

Question

Here is an assignment I was issued in Computer Science I [Visual Basic 2010]
Objective:
Modify the CalculatorII case study to display "ERROR" if a division by 0 is attempted. "ERROR should also be displayed if more than one decimal points are entered for a single number.
I can't get the ERROR message to show up when I divide by zero or add more decimal points. Here's what I have in coding:
Public Class Form1
Dim operand1 As Double = 0
Dim operand2 As Double = 0
Dim op As String = Nothing
Dim newOperand As Boolean = True
Private Sub Number_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles _
btnDot.Click, btn0.Click, btn1.Click, btn2.Click, btn3.Click, btn4.Click, btn5.Click, _
btn6.Click, btn7.Click, btn8.Click, btn9.Click
Dim btnNumberClicked As Button = sender
If newOperand Then
Me.txtDisplay.Text = btnNumberClicked.Tag
newOperand = False
Else
Me.txtDisplay.Text &= btnNumberClicked.Tag
End If
End Sub
Private Sub btnClear_Click(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles btnClear.Click
Me.txtDisplay.Text = "0"
operand1 = 0
operand2 = 0
newOperand = True
op = Nothing
End Sub
Private Sub btnOff_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles _
btnOff.Click
Application.Exit()
End Sub
Private Sub btnOperator_Click(ByVal sender As Object, ByVal e As System.EventArgs) _
Handles btnPlus.Click, btnMinus.Click, btnTimes.Click, btnDivide.Click, btnEqual.Click, btnIntDivide.Click
Dim operatorSelected As Button = sender
If (operand1 = 0 And op = Nothing) Or op = "=" Then
operand1 = Val(Me.txtDisplay.Text)
ElseIf (operand1 = 0 And op = "/") Then
MessageBox.Show("ERROR")
Else
operand2 = Val(Me.txtDisplay.Text)
operand1 = Calculate(operand1, operand2, op)
Me.txtDisplay.Text = operand1
End If
op = operatorSelected.Tag
newOperand = True
End Sub
Function Calculate(ByVal firstOperand As Double, ByVal secondOperand As Double, _
ByVal op As String) As Double
Select Case op
Case "+"
Return (firstOperand + secondOperand)
Case "-"
Return (firstOperand - secondOperand)
Case "X"
Return (firstOperand * secondOperand)
Case "/"
Return (firstOperand / secondOperand)
Case "\"
End Select
End Function
End Classenter code here

Answer 1

Operand 2 has to be the error-field, you just check if the first operand is 0
change
"ElseIf (operand1 = 0 And op = "/") Then
to ElseIf (operand2 = 0 And op = "/") Then
Give it a try :)