Visual Basic

[Гостомысл]

пожалуйста, подскажите, как отладить программу.
Private Sub CommandButton1_Click()
Dim A, B, C, D, F As Single
A = InputBox(" введите вторую переменную")
B = InputBox(" введите третью переменную")
C = InputBox(" введите четвёртую переменную")
F = InputBox(" введите первую переменную")
TextBox1 = F
TextBox2 = B
TextBox3 = A
TextBox4 = C
If (B + A) - F - C Then TextBox5 = D
TextBox1 = " "
TextBox2 = " "
TextBox3 = " "
TextBox4 = " "
End If
End Sub

[gaw4]

1) Dim A, B, C, D, F As Single-----Dim A As Single, B As Single, C As Single, D As Single, F As Single
2)If (B + A) - F - C=? Then TextBox5 = D