Learn Visual Basic 6.0

4. More Exploration of the Visual Basic Toolbox

Example 4-1: Temperature Conversion

Start a new project. In this project, we convert temperatures in degrees Fahrenheit (set using a scroll bar) to degrees Celsius. As mentioned in the Review and Preview section, you should try to build this application with minimal reference to the notes. To that end, let's look at the project specifications.

Temperature Conversion Application Specifications

The application should have a scroll bar which adjusts temperature in degrees Fahrenheit from some reasonable minimum to some maximum. As the user changes the scroll bar value, both the Fahrenheit temperature and Celsius temperature (you have to calculate this) in integer format should be displayed. The formula for converting Fahrenheit (F) to Celsius (C) is:

To convert this number to a rounded integer, use the Visual Basic CInt() function. To change numeric information to strings for display in label or text boxes, use the Str() or Format() function. Try to build as much of the application as possible before looking at my approach. Try incorporating lines and shapes into your application if you can.

One Possible Approach to Temperature Conversion Application:

Place a shape, a vertical scroll bar, four labels, and a command button on the form. Put the scroll bar within the shape - since it is in the top-layer of the form, it will lie in the shape. It should resemble this:

Set the properties of the form and each object:

Form1:	BorderStyle	1-Fixed Single
	Caption	Temperature Conversion
	Name	frmTemp
Shape1:	BackColor	White
	BackStyle	1-Opaque
	FillColor	Red
	FillStyle	7-Diagonal Cross
	Shape	4-Rounded Rectangle
VScroll1:	LargeChange	10
	Max	-60
	Min	120
	Name	vsbTemp
	SmallChange	1
	Value	32
Label1:	Alignment	2-Center
	Caption	Fahrenheit
	FontSize	10
	FontStyle	Bold
Label2:	Alignment	2-Center
	AutoSize	True
	BackColor	White
	BorderStyle	1-Fixed Single
	Caption	32
	FontSize	14
	FontStyle	Bold
	Name	lblTempF
Label3:	Alignment	2-Center
	Caption	Celsius
	FontSize	10
	FontStyle	Bold
Label4:	Alignment	2-Center
	AutoSize	True
	BackColor	White
	BorderStyle	1-Fixed Single
	Caption	0
	FontSize	14
	FontStyle	Bold
	Name	lblTempC
Command1:	Alignment	2-Center
	Cancel	True
	Caption	E&xit
	Name	cmdExit

Note the temperatures are initialized at 32F and 0C, known values.

When done, the form should look like this:

Temperature Conversion

Put this code in the general declarations of your code window.

Option Explicit
Dim TempF As Integer
Dim TempC As Integer

This makes the two temperature variables global.
Attach the following code to the scroll bar Scroll event.

Private Sub vsbTemp_Scroll()
'Read F and convert to C
TempF = vsbTemp.Value
lblTempF.Caption = Str(TempF)
TempC = CInt((TempF - 32) * 5 / 9)
lblTempC.Caption = Str(TempC)
End Sub

This code determines the scroll bar Value as it scrolls, takes that value as Fahrenheit temperature, computes Celsius temperature, and displays both values.
Attach the following code to the scroll bar Change event.

Private Sub vsbTemp_Change()
'Read F and convert to C
TempF = vsbTemp.Value
lblTempF.Caption = Str(TempF)
TempC = CInt((TempF - 32) * 5 / 9)
lblTempC.Caption = Str(TempC)
End Sub

Note this code is identical to that used in the Scroll event. This is almost always the case when using scroll bars.
Attach the following code to the cmdExit_Click procedure.

Private Sub cmdExit_Click()
End
End Sub
Give the program a try. Make sure it provides correct information at obvious points. For example, 32 F better always be the same as 0 C! Save the project - we�ll return to it briefly in Class 5.

Other things to try:
- Can you find a point where Fahrenheit temperature equals Celsius temperature? If you don't know this off the top of your head, it's obvious you've never lived in extremely cold climates. I've actually witnessed one of those bank temperature signs flashing degrees F and degrees C and seeing the same number!
- Ever wonder why body temperature is that odd figure of 98.6 degrees F? Can your new application give you some insight to an answer to this question?
- It might be interesting to determine how wind affects perceived temperature - the wind chill. Add a second scroll bar to input wind speed and display both the actual and wind adjusted temperatures. You would have to do some research to find the mathematics behind wind chill computations. This is not a trivial extension of the application.

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