CSE 100: Lab, April 15

A Closer Look at the VB Code Window

The code shown here is "Latte, Sample Solution 2," available in the File Archive.

Control names for frmLatte

option buttons:
optShort, optTall, optGrande




label:
lblShots

text box:
txtShots

 label:
lblPrice (barely visible)




command button:
btnCalculatePrice

The code for frmLatte

Key things to remember about the code window

a roadmap of the code

remarks code
At the very beginning of your code, you should always have the Option Explicit line, which is your way of promising Visual Basic that before you use any variable, you'll declare it. (see p. 158 in the red book and the April 13 lab handout)

Any variable declarations (Dim lines) you put here are for global variables (see April 13 lab handout), since they're not inside a procedure. In this case, the Dim line declares one global variable called size for storing strings.

Option Explicit
Dim size As String
Here's the first of the five subroutines in this code; note the header and trailer lines.

This Sub, called btnCalculatePrice_Click, is an event handler, where the "event" is clicking the Calculate Price button. The code in this Sub is run each time the user clicks the button control named btnCalculatePrice_Click.

The IDE sets up the header and trailer lines for this Sub when you create and double-click the button control on your form

Note the three variable declarations at the start of this Sub. These are local variables and can only be used inside this Sub.

There are two variable assignments, one for shots and another for price. Between them is a call to another Sub called calcPrice, defined below.

The last line looks a lot like a variable assignment, but what's doing is changing a property of a control. In this case, the Caption property of the label control called lblPrice.

 
Private Sub btnCalculatePrice_Click()
    Dim shots As Integer
    Dim subTotal As Single
    Dim price As Single

    shots = txtShots.Text
    Call calcPrice(subTotal, shots, size)
    price = subTotal + subTotal * 0.086

    lblPrice.Caption = "$" & Round(price, 2)
End Sub
This Sub, unlike the last one, is not an event handler. The programmer had to type the header line in by hand.

Again, we see some local variable declarations, and most of the code is composed of conditionals, three little conditionals (Ifs) and a fourth for extra charge which uses If with Else.

Note the assignment at the end: p is basically whatever variable was passed as the first parameter in the call. (In the case of the call above in btnCalculatePrice_Click(), this is subTotal. Since subTotal is passed by reference, this assignment actually changes the value stored in subTotal when this Sub is called.

 
Sub calcPrice(p As Single, sh As Integer, sz As String)
    Dim basePrice As Single
    Dim extraCharge As Single

    If sz = "short" Then
        basePrice = 1.1
    End If

    If sz = "tall" Then
        basePrice = 1.5
    End If

    If sz = "grande" Then
        basePrice = 1.9
    End If

    If sh > 1 Then
        extraCharge = (sh - 1) * 0.65
    Else
        extraCharge = 0
    End If

    p = basePrice + extraCharge
End Sub
Finally, we have three similar Subs, all of which are event handlers. These Subs are called when the three option buttons for choosing latte size are clicked.

Each contains just a single assignment to the global variable size.

 
Private Sub optGrande_Click()
    size = "grande"
End Sub


Private Sub optShort_Click()
    size = "short"
End Sub


Private Sub optTall_Click()
    size = "tall"
End Sub