Simple VBA calculation

[snb]

other approaches:

Private Sub UserForm_Click()
    MsgBox Application.Sum(Array(Val(TextBox1), Val(TextBox2), Val(TextBox3), Val(TextBox4)))
End Sub

Private Sub UserForm_Click()
    MsgBox Evaluate("sum(" & TextBox1 & "," & TextBox2 & "," & TextBox3 & "," & TextBox4 & ")")
End Sub