yet another calculator problem

[Anarchist]

I am a beginner and am trying to make a calculator, i need some help with the BuildNumber, could someone show me how I can use this method to add the button clicked to the string please.

Private Sub BuildNumber(Number As String)
'Adds a number to the expression string
    
End Sub

Private Sub cmd0_Click()
'add number to string
Call BuildNumber("0")
txtOutput.Text = "0"
End Sub

Private Sub cmd1_Click()
'add number to string
  Call BuildNumber("1")
 txtOutput.Text = "1"
End Sub

Private Sub cmd2_Click()
'add number to string
  Call BuildNumber("2")
  txtOutput.Text = "2"
End Sub

Private Sub cmd3_Click()
'add number to string
  Call BuildNumber("3")
  txtOutput.Text = "3"
End Sub

Private Sub cmd4_Click()
'add number to string
  Call BuildNumber("4")
  txtOutput.Text = "4"
End Sub

Private Sub cmd5_Click()
'add number to string
   Call BuildNumber("5")
  txtOutput.Text = "5"
End Sub

Private Sub cmd6_Click()
'add number to string
 Call BuildNumber("6")
 txtOutput.Text = "6"
End Sub

Private Sub cmd7_Click()
'add number to string
 Call BuildNumber("7")
 txtOutput.Text = "7"
End Sub

Private Sub cmd8_Click()
'add number to string
 Call BuildNumber("8")
 txtOutput.Text = "8"
End Sub

Private Sub cmd9_Click()
'add number to string
 Call BuildNumber("9")
 txtOutput.Text = "9"
End Sub

Thanks
Anarchist