Learning VBA: Need Some Explanations on Language

[Agimcomas]

Hi.
I'm new to this forum so let me introduce myself. I am a final year undergraduate in Finance and I'm teaching myself VBA programming to be ready to enter the job market.

I have a copy of "Option Pricing Models & Volatility Using Excel-VBA" and I'm going through the examples in the first chapter.

Let me show you the code:

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I should probably show you one of the previous functions in the program:

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Now, I understand most of the code, but I still don't have a clue on the following:

1. Is cNum a variable type?
2. What does setcnum() mean?
3. What do .rP and .iP mean? What is the syntax?
4. What does the line "complexop2 = output" exactly do?

I hope that somebody can help me out. Thanks in advance!

[Leith Ross]

Hello Agimcomas,

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[tony h]

I can only answer this partially and I may have missed bits.

Is cNum a variable type? it is a class type. Dim cNum1 As cNum defines a variable cNum1 to be of type cNum.

What does setcnum() mean? Setcnum is the function that you have defined in your second piece of code

What do .rP and .iP mean? What is the syntax? these are properties of another class

What does the line "complexop2 = output" exactly do? Output was defined (Dim statement) as a 2 element array containg doubles. This makes the function complexop2 return this doublex2 array

[6StringJazzer]

Since you are new at this let me try to give a somewhat more detailed explanation, although without the book you are looking at it's hard to give gobs of detail.

1. Is cNum a variable type? It is either a user-defined variable, or a class. A user-defined variable can have subfields. Here's an example from Excel Help:

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You declare variables using it as a type, just like any other type. More on this in #3.

2. What does setcnum() mean? I am assuming you made a typing error and this is actually Set_cNum. It is a function call. When you call a function, the call is replaced at runtime by the value returned by the function. See more at #3.

3. What do .rP and .iP mean? What is the syntax? rP and iP are subfields of the data type (or possibly members of the class) cNum. If you declare a variable

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then you can refer to the subfields of that variable with the dot notation as in this example:

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In the code where you are seeing this, they are used after the function name, which bears additional explanation. When you see

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it means this function is going to return an item that is type cNum. A function always returns a variable that is the same as the function name. So this line of code means that the function Set_cNum is going to return a variable of type cNum that has its rP subfield set to rPart, which also happens to be an argument for the function. So this function has the purpose of taking two values, and packaging them up into a single cNum variable.

4. What does the line "complexop2 = output" exactly do? The function Complexop2 does not explicitly declare what data type it returns (poor practice, IMHO) so it defaults to Variant. So it can return any data type. In this case, it is being assigned the variable output, an array with two elements of type Double.

[Agimcomas]

Thank you for your prompt answers.

I am assuming you made a typing error and this is actually Set_cNum. It is a function call. When you call a function, the call is replaced at runtime by the value returned by the function.

I am also confused by this, because the code is actually written like this in the book. I assume the authors made a mistake.

You really helped me out.

Regards!

[Agimcomas]

I have another doubt:

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What is Run?

Thanks!

[6StringJazzer]

It is a function. I don't like to give an "I don't know" answer but in this case I could not find a built-in function called Run so I can only assume it is a function defined somewhere else in the code you are looking at.

[shg]

Run is an application method, and is incorrect in the context you show. If it's the name of a function, it shouldn't be.

[6StringJazzer]

Run is an application method, and is incorrect in the context you show. If it's the name of a function, it shouldn't be.

I was unfamiliar with Application.Run but after I looked it up I'm convinced that what is intended here. It will run the macro whose name is set in fname and pass in a or b (as appropriate) as a parameter.

fname itself is passed into BisMet as a parameter. So the code calling BisMet is deciding at runtime what function that BisMet should call. I don't know how BisMet is called so I can't shed any additional light on what is really going on.

This is a level of indirection I don't recommend. It's just a little too clever, IMHO. It is confusing just to look at the code statically and figure out how it works, and it is doubly confusing to diagnose a problem at runtime. This is what we used to call "control coupling" (not a good kind of coupling). People do stuff like this in C with procedure pointers but it gets tangled quickly.

[stanleydgromjr]

Agimcomas,

Training / Books / Sites:

How to Learn to Write Macros
http://articles.excelyogi.com/playin...ba/2008/10/27/

How to use the macro recorder
http://articles.excelyogi.com/

Click here and scroll down to Getting Started with VBA.
http://www.datapigtechnologies.com/ExcelMain.htm

If you are serious about learning VBA try
http://www.add-ins.com/vbhelp.htm

Excel Tutorials and Tips - VBA - macros - training
http://www.mrexcel.com/articles.shtml

See David McRitchie's site if you just started with VBA
http://www.mvps.org/dmcritchie/excel/getstarted.htm

Debra Dalgleish has some notes how to implement macros here:
http://www.contextures.com/xlvba01.html

David McRitchie has an intro to macros:
http://www.mvps.org/dmcritchie/excel/getstarted.htm

Ron de Bruin's intro to macros:
http://www.rondebruin.nl/code.htm

Creating custom functions
http://office.microsoft.com/en-us/ex...117011033.aspx

Writing Your First VBA Function in Excel
http://www.exceltip.com/st/Writing_Y...Excel/631.html

http://www.excel-vba.com/
http://www.mvps.org/dmcritchie/excel/getstarted.htm
http://www.exceltip.com/excel_links.html

(livelessons video)
Excel VBA and Macros with MrExcel
ISBN: 0-7897-3938-0
http://www.amazon.com/Excel-Macros-M...7936479&sr=1-1

http://www.xl-central.com/index.html

http://www.datapigtechnologies.com/ExcelMain.htm

Dependent validation lists. Debra has a neat little tutorial here.
http://www.contextures.com/xlDataVal02.html

Cascading queries
http://www.tushar-mehta.com/excel/ne...ing_dropdowns/

http://www.contextures.com/xlDataVal05.html

Programming The VBA Editor - Created by Chip Pearson at Pearson Software Consulting LLC
This page describes how to write code that modifies or reads other VBA code.
http://www.cpearson.com/Excel/vbe.aspx

Locating files containing VBA
Searching Files in Subfolders for VBA code string:
http://www.dailydoseofexcel.com/arch...a-code-string/

http://www.pcreview.co.uk/forums/thread-978054.php

Excel 2003 Power Programming with VBA, by John Walkenbach

VBA and Macros for Microsoft Excel, by Bill Jelen "Mr.Excel" and Tracy Syrstad

Excel Hacks 100 Industrial-Strength Tips & Tools, by David & Traina Hawley

VBA and Macros for Microsoft Excel 2007, by Bill Jelen "Mr.Excel" and Tracy Syrstad

Excel 2007 Book: you can try this...there is a try before you buy ebook available at this link…
http://www.mrexcel.com/learnexcel2.shtml

DonkeyOte: My Recommended Reading:

Volatility
http://www.decisionmodels.com/calcsecretsi.htm

Sumproduct
http://www.xldynamic.com/source/xld.SUMPRODUCT.html

Arrays
http://www.xtremevbtalk.com/showthread.php?t=296012

Pivot Intro
http://peltiertech.com/Excel/Pivots/pivotstart.htm

Email from XL - VBA
http://www.rondebruin.nl/sendmail.htm

Outlook VBA
http://www.outlookcode.com/article.aspx?ID=40

Function Dictionary
http://www.xlfdic.com/

Function Translations
http://www.piuha.fi/excel-function-name-translation/

Dynamic Named Ranges
http://www.contextures.com/xlNames01.html

And, as your skills increase, try answering posts on sites like:
http://www.mrexcel.com/
http://www.excelforum.com/
http://www.ozgrid.com/
http://www.vbaexpress.com/portal.php
http://p2p.wrox.com/excel-vba-79/