More Chapter 3 Method questions.

wbrco · February 13th, 2009, 12:05 PM

First a little background -
My first programming course punched cards for SYS370 in FORTRAN, and years (and years) ago, I did some TurboC. (in fact, for you Borland/CodeGear folks, Allan Bauer used to be my roomate and co-worker, but I could never get my brain around Pascal..) However, my career never really required me to do much
programming. I'm finding now that it's becomming more of a requirement to stay competative.

*SO*

Working on the Building a Method Try it Out on P.79. Worked ok as the book instructed, but I got the fancy idea of why not make the messagebox a sub as well, and why not make dblArea a public var? (cobbwebs getting brushed away in the back of my brain..).

So, I came up with this with AreaMessageBox() as a sub as well.

PublicClass Form1
'declare dblArea as public var
Dim dblArea AsDouble
PrivateSub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
'calculate the area of a circle with radius of 100
dblArea = CalculateAreaFromRadius(100)
'display the results
AreaMessageBox(dblArea)
EndSub
PrivateSub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
'Calculate the area of a circle with radius of 25
dblArea = CalculateAreaFromRadius(25)
'display the results
AreaMessageBox(dblArea)
EndSub
PrivateSub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
'calculate area of circle with radius of 250
dblArea = CalculateAreaFromRadius(250)
'display the results
AreaMessageBox(dblArea)
EndSub
'Calculate area from radius - find the area of a circle
PrivateFunction CalculateAreaFromRadius(ByVal radius AsDouble) AsDouble
'declare variables
Dim dblRadiusSquared AsDouble
Dim dblResult AsDouble
'square the radius
dblRadiusSquared = radius * radius
'multiply by pi
dblResult = dblRadiusSquared * Math.PI
'return the result
Return dblResult
EndFunction
'Area Messagebox sub
PrivateFunction AreaMessageBox(ByRef dblArea AsDouble)
'display message box for the area calucations for each button click
MessageBox.Show("The area of the circle is " & dblArea.ToString, "Circle Area")
Return (dblArea)
EndFunction
EndClass

I pass dblArea to AreaMessageBox, and everything works. But WHY do I need to pass dblArea back as part of the return statement? I really don't need it. How can I get it to pass back a null or T/F of sub completion?

Thanks!
Allen

dparsons · February 16th, 2009, 02:07 PM

Based on the code you have presented here AreaMessageBox should be a method and not a function since the value that is returned is never used to evaluate anything or used otherwise.

Now my statement is based soley on the code you have presented here and since I have not read the book in question, I would exercise caution in changing this to a method if this sample is something the author builds on later in the book where AreaMessageBox needs to return a value for some reason.

Outside of that, I see no reason why this shouldn't be a method.

hth.
-Doug

wbrco · February 16th, 2009, 11:39 PM

Quote:

Originally Posted by dparsons

Based on the code you have presented here AreaMessageBox should be a method and not a function since the value that is returned is never used to evaluate anything or used otherwise.

Now my statement is based soley on the code you have presented here and since I have not read the book in question, I would exercise caution in changing this to a method if this sample is something the author builds on later in the book where AreaMessageBox needs to return a value for some reason.

Outside of that, I see no reason why this shouldn't be a method.

hth.
-Doug

So, I guess I don't get the difference between a method and a function. In my mind, they are both subroutines, so I don't see the distinction. In C, there is no distinction. Maybe I need to read some more of the book, or you (or anybody else) and explain?

I went and pulled out my old C book ("The Waite Group's TurboC Programming for the PC Revised Edition, Copywrite 1989) to confirm that. I'm trying to NOT do this as I'm afraid that it will only confuse me more!

Thanks!
Allen

dparsons · February 17th, 2009, 12:14 AM

Hi Allen!

As far as the difference between a Subroutine and Function go it is really quite simple. A sub routine simply DOES something where as a Function RETURNS something. So you write a sub when you need to do something but arent expecting a return value (e.g. a method to save info to a database) and you would use a function when you need to do some further processing with the return value (when you are returning data from a database for example).

Does that make sense?

hth.
-Doug