Functions and Subroutines

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Functions and Subroutines

• 3/10/2003

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More about Arrays

• Key word Redim
• Dim SomeArray() as SomeType
• intSomeNumber 28 (some value)
• Redim SomeArray(intSomeNumber) as SomeType
• Keep track of array size
• Declare array size at the form level
• Keep track of it all the time when you add a
  new element, increase it by one when you delete
  an element, decrease it by one.

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Using General Procedures

• Event procedures are associated with a particular
  event and are not usually available to other
  forms.
• General procedures are used for specific tasks
  that are not associated with an event.
• General procedures are defined in the General
  Object of a form and then invoked elsewhere in
  the project.
• Write it once and make it available at every spot
• Two types of general procedures
• subs (subroutines)
• functions

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Why General Procedures ?

• Divide and Conquer break complexity into parts
• Keep a general purpose task done in one piece of
  code, reuse it every time its needed

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Built-in Programmer-defined

• Weve used Provided procedures
• Functions IsNumeric(), Eof(), Date
• Subs like Msgbox, Format( string, format)
• You can write functions too
• 1. Break complexity into pieces
• 2. Avoid repeating stuff
• 3. Parameterize re-useable code

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Creating a Function

• The general form of the function definition
  statement is
• Function intFindMax(intNum1 as Integer, intNum2
  as Integer) as Integer
• logic
• End Function
• The function definition defines f(x), type of
  output, type and number of inputs
• An important rule is that the name of the
  function must be assigned a value in the function
  definition this value will be returned to the
  calling procedure (assigned to y)

• Mathematical function y f(x) three pieces
• The function definition in terms of x
• E.g. f(x) pi x2
• F(x) 2 pi x
• The input x
• Assign the function value to the output y

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Subs and Functions

• A sub is a unit of code that performs a specific
  task but returns no value.
• A function is similar to the built in functions
  in that arguments are passed to it and processed
  to compute a single value returned by its name.

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Design a general procedure

• Decide
• what the we want it to do
• What input and desired output are
• What logic is required to convert the input into
  the desired output
• Input is usually through the arguments
• Output for a function is usually through its
  name, and output from a sub is usually through
  the arguments

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Creating a Sub

• The general form of the sub definition statement
  is
• Sub SubName (parameter1 as type, parameter2 as
  type, )
• End Sub
• Note that the sub name is not assigned a data
  type, because it is not the sub itself what is
  going to be returned, the return is through the
  argument(s)
• Example
• Sub Switch(curFirst as Currency,curSecond as
  Currency)
• lotic
• End Sub

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Creating Subs and Functions

• To create a sub or function you can
• Use the ToolsAdd Procedure menu command and
  select the type of procedure to add
• or
• simply type the word Sub or Function and press
  Enter after any existing event or general
  procedure.
• In either case, then add the parameters in
  parentheses.

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Invoking a General Procedure

• General procedures must be created and then
  invoked.
• Arguments in the definition and parameters passed
  to the procedure are nothing but variable names.
• Invoking a function assign the function to a
  variable
• variable functionname(arg1, arg2, , argn)
• Invoking a sub
• subname arg1, arg2, , argn
• Or
• Call SubName (arg1, arg2, , argn)

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Using a General Procedure

• The name of the arguments and parameters need not
  be the same its the order that is important
• A general procedure can be used with different
  arguments as long as the arguments match the
  parameters
• The product of a sub procedure depends on the
  ingredients (arguments) passed to it

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Example - Sub Procedure

• Sub MixBake (ingredient 1, ingredient 2,
  ingredient 3)
• 1. Mix ing1 2
• 2. Stir the mixture of step 1 for two minutes
• 3. Put mixture in ing3 and bake for 15 minutes
• 4. Put product in ing3
• End Sub

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Using the Procedure

• What I get also depends on the order of the
  arguments I pass
• Call MixBake baking pan, flour, milk
• Baked mixture of flour and baking pan is returned
  in milk!
• That is NOT what I want!
• Too bad. But that is what you asked the computer
  to do.

• What I get depends on what I pass to the
  procedure
• Call MixBake flour, milk, baking pan
• A cake is returned in the baking pan
• Call MixBake chemical 1, chemical 2, pan
• A new chemical is returned in the pan

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Relationship Between Sub Definition Statement and
Statement Invoking the Sub
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Relationship Between Function Definition
Statement and the Statement Invoking the Function
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Matching Arguments and Parameters

• For both sub and functions, the number, type, and
  order of arguments in the invoking statement must
  match the number, type, and order of parameters
  in the procedure definition statement. Note that
  the names of the variables do NOT need to match.

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Array Arguments

• In both the argument and parameter list,
  fixed-size arrays are referenced by the name of
  the array followed by parentheses.
• Pass array size as an argument to the procedure
• Sub definition
• Sub Sort(intNumber as Integer, strList() as
  String)
• Calling statement
• Sort intNumCustomers, strCustomers()

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Global Declarations and the Code Module

• A Code Module is a section of pure code that is
  known to all parts of the project.
• Use Public statement to declare variables
• Public varName1 as type, varName2 as type, ...
• When variables are declared in a code module
  using key word public, they are known to the
  entire project in contrast to form-level or
  procedure level variables that are known only to
  the form or to the procedure

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Scope of Global Variables
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Assignment D

• It is hard lots of work new material much of
  it from chapter 7 none from chapter 8
• Do you wait until you know enough?
• Doesnt seem like a good idea
• How do you start before you know enough?
• ?by doing things you already know how to do
• What are they?

Borrowed from Dr. Madeo
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What are They?

• Putting things on a form
• Deciding which events require implementation
• This must includes click events for each command
  button
• Of course, you can see the command buttons when
  you execute the .exe file
• You may know what it to happen during each of them

Borrowed from Dr. Madeo
23

• If you arent ready to write all the code, write
  what you can and place comments describing whats
  to be done
• To the extent possible, RUN what you have. Itll
  get rid of syntax errors and maybe some simple
  logic errors

Borrowed from Dr. Madeo
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• In particular, you ought to test out the process
  of going from form to form and make sure it
  works.
• You should put your name on each form
• You should put every part of what you are doing
  in a folder whether it be on a floppy, a zip
  disk, your N drive,
• I often start a project this way

Borrowed from Dr. Madeo
25

• Getting an early start is particularly important
  if you have decided not to be in class on one or
  both of Fri. 3/14 and Mon. 3/24
• We will definitely post a solution prior to Exam
  Three on April 2 it is not as clear that the
  assignments will be graded before the exam

Borrowed from Dr. Madeo
26
Executive Summary

• Its due on Monday, March 31
• The good news was that we moved back the due date
  on Assignment D giving you more time
• The bad news is that you dont have lots of time
  AFTER Assignment D to do the Executive Summary

Borrowed from Dr. Madeo
27

• We are serious about two elements of the
  executive Summary
• 1. The time it is due. Dont be late.
• 2. The length. The body of the paper is not to
  exceed two pages.
• The body of the paper does not include
• The optional cover page with your name
• The non-optional list of 5 or more references no
  more than 40 of which can be purely from the
  web. You might se the sources of full text
  online availability of articles through the
  techy stuff in the library
• Of course, it is expected that your summary will
  exceed 1.5 pages

Borrowed from Dr. Madeo
28
Final Exam Time

• Although it is possible that there will be a
  last minute denial, we have been told to act as
  if our request for having a common 4600 exam on
  Tuesday, May 6 from 7 to 10 p.m. has been
  approved.
• If you have a conflict, please see me as soon as
  possible

Borrowed from Dr. Madeo