giving calculator input from keyboard keys without pressing calculator buttons - vb.net

Question

I created a VB.net calculator application.It works fine but say I want to add 5+7.Then as my application works I can press 5 from the keyboard as I gave the text of button with digit 5 as &5 but then if I press + from the keyboard it doesn't work.I have to press the + button in the calculator.
I think that's because my add button is designed to handle click event as btn_add_Click.Is there a way I can make this application to work so that without pressing the buttons in the calculator I can press the keys in keyboard and do the computation.Here's my code:
Imports System.Math
Public Class Form1
Private isFirstExist As Boolean
Private inputOperator As String
Private secondNum As Decimal
Private firstNum As Decimal
Private Sub TextBox1_TextChanged(sender As System.Object, e As System.EventArgs) Handles txtCalc.TextChanged
End Sub
Private Sub btn_zero_Click(sender As System.Object, e As System.EventArgs) Handles btn_zero.Click
removeFrontZero(0)
End Sub
Private Sub btn_one_Click(sender As System.Object, e As System.EventArgs) Handles btn_one.Click
removeFrontZero(1)
End Sub
Private Sub btn_two_Click(sender As System.Object, e As System.EventArgs) Handles btn_two.Click
removeFrontZero(2)
End Sub
Private Sub btn_clear_Click(sender As System.Object, e As System.EventArgs) Handles btn_clear.Click
txtCalc.Clear()
txtCalc.Text = "0"
End Sub
'Remove zero which is at the start
Public Sub removeFrontZero(ByVal digit As Integer)
If txtCalc.Text = "0" Then
txtCalc.Text = CStr(digit)
Else
txtCalc.Text &= digit
End If
End Sub
Private Sub btn_add_Click(sender As System.Object, e As System.EventArgs) Handles btn_add.Click
inputOperator = "+"
isFirst()
End Sub
Private Sub Form1_Load(sender As System.Object, e As System.EventArgs) Handles MyBase.Load
isFirstExist = False
End Sub
Private Sub btn_equal_Click(sender As System.Object, e As System.EventArgs) Handles btn_equal.Click
If isFirstExist Then
secondNum = CType(txtCalc.Text, Decimal)
End If
'Calculating the result
Dim result As Decimal = calculate(firstNum, secondNum, inputOperator)
txtCalc.Text = result.ToString()
isFirstExist = False
End Sub
Private Function calculate(ByVal num1 As Decimal, ByVal num2 As Decimal, ByVal inputOp As String) As Decimal
Dim output As Decimal
firstNum = num1
secondNum = num2
Select Case inputOp
Case "+"
output = num1 + num2
Case "-"
output = num1 - num2
Case "/"
Dim value As Decimal
Try
isFirst()
value = (num1 / num2)
Catch ex As DivideByZeroException
MessageBox.Show(ex.Message, "Error", MessageBoxButtons.OK)
End Try
output = value
Case "*"
output = num1 * num2
Case "Mod"
output = (num1 Mod num2)
Case "^"
output = CDec(Math.Pow(num1, num2))
End Select
Return output
End Function
Private Sub isFirst()
If isFirstExist = False Then
firstNum = CType(txtCalc.Text, Decimal)
isFirstExist = True
txtCalc.Text = "0"
End If
End Sub

Answer 1

Assuming you're using the textbox to hold the users input, in the Textchanged or even KeyPressed handler trap the operator keys and run the function instead of displaying the operator.
Something like this:
Private Sub TextBox1_KeyPress(sender As Object, e As KeyPressEventArgs) Handles txtCalc.KeyPress
If e.KeyChar = "+"c Then
inputOperator = "+"
isFirst()
e.Handled = True
End If
End Sub
To display the operator set handled to false.