User defined functions

Report
259 Lecture 9 Spring 2013
Advanced Excel Topics – Visual Basic
for Applications (VBA)
VBA Topics
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Developer Tab
Form Controls
User Defined Functions
VBA Editor
Comments
Variable Data Types
Local Variables
Variable Assignment
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Form Controls
 Form controls consist of items seen in
windows programs and dialog boxes
such as buttons, scroll bars, spinners,
list boxes, check boxes, radio
buttons, …
 In order to be able to add form
control items, the “developer tab”
MUST be added.
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Adding the Developer Tab to
the Ribbon
 Windows: File,
Options,
Customize
Ribbon, Check
“Developer”
 Mac: Excel,
Preferences,
Ribbon, Check
“Developer”
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Add a List Box Control
 Example 1: Create
a worksheet that will
allow the user to
select an “Employee
Name” from a “list
box” and return the
corresponding
“Employee Number”.
Also highlight in
ORANGE, the
selected “Employee
Name” and
“Employee Number”.
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Add a List Box Control (cont.)
 Step 1: Create
an empty “List
Box” .
 Developer, Insert
(Icon), Form
Controls, List Box,
then Drag a
Rectangle
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Add a List Box Control (cont.)
 Step 2: Populate the
“List Box” with the input
items, and link the
output of the “List Box”
to a cell reference.
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Right-Click, Format
Control, Control, …
Input range: A1:A5
Cell Link: C1
Test the bi-directional
link between the “List
Box” and cell C1. Notice
how manually changing
cell C1 also updates the
“List Box” .
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Add a List Box Control (cont.)
 Step 3: Add a
formula to cell C2 to
get the “Employee
Number”
 =INDEX(B1:B5,C1,1)
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Add a List Box Control (cont.)
 Step 4: Add the
conditional formatting to
highlight in ORANGE, the
selected “Employee
Name” and “Employee
Number”.
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Select cell A1
Home, Styles, Conditional
Formatting, Manage
Rules, New Rule, Use a
formula to determine
which cells to format
=ROW()=$C$1
Use the “Format Painter”
to apply the Conditional
Format to the other cells.
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Add a Scroll Bar Control
 Example 2: Create a worksheet that
will decode a one word “Caesar
Cipher”. Allow the user to select the
“shift” value by using a “Scroll Bar”.
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Add a Scroll Bar Control (cont.)
 Step 1: Create a “Scroll Bar”
 Developer, Insert (Icon), Form Controls,
Scroll Bar, then Drag a Rectangle
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Add a Scroll Bar Control (cont.)
 Step 2: Set the
properties for the “Scroll
Bar”, and link the output
of “Scroll Bar” to a cell
reference.
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

Right-Click, Format
Control, Control, …
Minimum Value: 0 ;
Maximum Value: 25 ;
Incremental Value: 1 ;
Cell Link: O1
Test the bi-directional
link between the “Scroll
Bar” and cell O1. Notice
how manually changing
cell O1 also updates the
“Scroll Bar” .
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Add a Spinner Control
 Example 3: Create a worksheet that
will decode a one word “Caesar
Cipher”. Allow the user to select the
“shift” value by using a “Spinner”.
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Add a Spinner Control (cont.)
 Step 1: Create a
“Spinner”
 Developer, Insert
(Icon), Form
Controls, Spin
Button, then
Drag a Rectangle
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Add a Spinner Control (cont.)
 Step 2: Set the
properties for the
“Spinner”, and link the
output of “Spinner” to a
cell reference.

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
Right-Click, Format
Control, Control, …
Minimum Value: 0 ;
Maximum Value: 25 ;
Cell Link: O1
Test the bi-directional
link between the
“Spinner” and cell O1.
Notice how manually
changing cell O1 also
updates the “Spinner” .
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Add a Spinner Control (cont.)
 Example 4: Create a worksheet that will
decode a one word “Caesar Cipher”.
Allow the user to select the “shift” value
by using a “Spinner”. The worksheet
should indicate that the user has
“LOCKED” in on a “real” word by
highlighting the characters of the
decoded word in BLUE.
 Decode the following word: XDGOWJ
 Decode the following word: ZOYZVO
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Add a Spinner Control (cont.)
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Moving, Resizing, Deleting
Form Controls
 Right-Click on the
Form Control,
ESC
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Computer Program
 Def: A computer program or program is a
sequence of instructions that a computer can
interpret and execute. (from dictionary.com)
 Def: A computer program is one or more
instructions that are intended for execution by a
computer. Without programs, computers would
not run. Moreover, a computer program does
nothing unless its instructions are executed by a
central processor. Computer programs are the
result of the compilation or interpretation of
programming languages, are embedded into
hardware, or may be manually inputted to the
central processor of a computer. (from
Wikipedia)
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Computer Program (cont.)
 Software such as Excel, Mathematica, or
MATLAB can be can be used to write
computer programs when more than
single step or an iterative process is
required for some application or problem
that needs to be solved.
 There are many programming languages
that can be used to write computer
programs, including Visual Basic for
Applications.
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Visual Basic for Applications (VBA)
 BASIC – Beginners All Purpose Symbolic
Instruction Code (1960)
 Visual Basic for Windows – Introduced by
Microsoft in 1991, GUI interface, OOP – Object
Oriented Programming
 Visual Basic for Applications – Introduced by
Microsoft (Excel 5) as a common scripting
language for Word, Excel, Power Point, and
Access.
 VBA is “BIG” and takes years to completely
master.
 We are getting a “CRASH” course in VBA dealing
specifically with “User Defined Functions”.
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Visual Basic (VB) Editor
 Add in the
Developer Tab
 File, Options,
Customize
Ribbon, Main
Tabs, Developer
 Start the Visual
Basic Editor
 Press ALT+F11 or
Developer Tab,
“Visual Basic”
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User Defined Functions (UDF)
 User defined functions (UDF), are
functions created by the user, but
behave just like built in Excel
functions.
 User defined functions are written in
VBA code.
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User Defined Functions (cont.)
 Example 5: Create a “Hello World”
user defined function (UDF) named
Hello_World() that accepts no
arguments and returns the phrase
“Hello World”.
 For example, entering the formula
=Hello_World() into cell A1, will
produce “Hello World” in cell A1.
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User Defined Functions (cont.)
 VBA code:
Function Hello_World() As String
Hello_World = “Hello World”
End Function
 VBA code must be stored in a “Module”
which is a place for holding related VBA
functions and sub-routines.
 In this example, the UDF Hello_World()
will be stored in a module named:
“First_Program”.
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Steps to create the Hello_World()
user defined function
1.
2.
3.
4.
5.
6.
7.
8.
9.
Activate the VBA Editor.
Insert, Module
Enter the VBA code
Insert “Option Explicit” at the
very top before any function or
subroutine declarations. MAKES
SURE THAT ALL VARIBLES ARE
DEFINED … GIVES ERROR IF
NOT ALL DEFINED
Click on “Module1”, change
“(name)” property from
“Module1” to “First_Program”
Save
File, “Close and Return to
Microsoft Excel”
Use the function Hello_World()
just like any other built-in Excel
function.
Save the worksheet as a “MacroEnabled Workbook”
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Fahrenheit to Celsius UDF
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
Example 6: Create a user
defined function F_To_C()
that will convert a
temperature given and
degrees Fahrenheit and
return the equivalent
temperate in degrees
Celsius.
For example, =F_To_C(32)
should return 0 and
=F_To_C(212) should
return 100.
VBA code:
Function F_To_C(F As Double) As Double
F_To_C = 5/9*(F-32)
End Function
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Recalculating User Defined
Functions
 The F9 key is used to
recalculate all
worksheets in all open
workbooks.
 Pressing the F9 key will
not cause “User Defined
Functions” to recalculate.
 By default,
CTRL+ALT+F9 must be
pressed to “force” all
formulas to be
recalculated.
 It is important to press
CTRL+ALT+F9 after
making changes to the
VBA code of a UDF.
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Line Continuation
 Use the _ character for line continuation.
 As an example, the following code is “too
long” for a single line:
Function PerpBisectorIntercept(x1 As Double, y1 As Double, x2 As Double, y2 As Double) As Double
 To make code more “readible”, use multiple
lines for VBA code, via the _ character.
Function PerpBisectorIntercept(x1 As Double, _
y1 As Double, _
x2 As Double, _
y2 As Double) As Double
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Inserting Comments
 Comments are ignored by VBA.
 They are notes intended to be read by humans.
 Comments begin with a single quote character ‘ or
rem.
 Comments are often used for the following purposes:
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

Use comments to describe briefly the purpose of the user
defined function.
Use comments to describe changes made to the user
defined function.
Use comments to indicate that you are using functions or
code in an unusual or non-standard manner.
Use comments to describe the purpose of variables so that
you and other people can decipher otherwise cryptic
names.
Use comments to “temporarily” disable lines of VBA code.
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Inserting Comments (cont.)
 Example 7: Add comments to the
following user defined function to help
make the VBA code more “readable” :
Function Perp_Bisector_Slope(x1 As Double, y1 As Double, x2 As Double, y2 As Double) As Double
'Returns the slope of the line that is the "perpendicular bisector" of the line segment
'determined by points (x1,y1) and (x2,y2)
'The function does NOT work for vertical lines
Dim m1 As Double, m2 As Double
m1 = (y2 - y1) / (x2 - x1)
'negative reciprocal of m1
m2 = -1 / m1
Perp_Bisector_Slope = m2
End Function
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Variable Data Types
 A variable’s data type determines
both the type of information that can
be stored, and also the amount of
computer memory taken.
 The next slide contains a “condensed”
list of the data types available in
VBA:
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Variable Data Types (cont.)
Type
Boolean
Double
Integer
String
Variant
What the Variable
Can Hold
True or False
-12.42424, 3.156788,
-12, 12
Integers in the
interval
[-32768, 32767]
“Toad” , “12” , “-12” ,
“12.2” , “True”
True, “Toad”,
-12.24252, -12,
<object>
What the Variable
Can’t Hold
12, -12, -12.2, 12.2,
“Toad” , <object>
“Toad” , True, False,
<object>
Amount of Memory
the Variable Takes
2 Bytes
8 Bytes
12.2, -12.2, “Toad”,
True, <object>
2 Bytes
12, -12, True, 12.2,
<object>
(Length of the String)
in Bytes
(16+) Bytes
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Why not use the “Variant” data
type all of the time?
1. People reading VBA code may consider the
unnecessary use of “variant” as “sloppy”
programming.
2. The “Variant” data type is a memory “hog”
that takes away from system resources.
3. The “Variant” data type “slows” down
program execution speed. This is
important when VBA code is doing “many”
iterations.
4. Use the “Variant” data type only when it is
“needed”.
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Arguments to a User Defined
Function
 The arguments to a user defined
function are the variable(s) located
inside of the parenthesis.
 Arguments can be thought of as a
user defined function’s “input(s)”.
 To specify the data type for an
argument, place the word “As”
immediately after the variable name
followed by the data type.
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Arguments to a User Defined
Function (cont.)
 Examples:
Function F_To_C(F As Double) As Double
Function Perp_Bisector_Slope(x1 As Double, y1 As Double, x2 As Double, y2 As Double) As Double
Function Quadratic_1(A As Double, B As Double, C As Double) As Double
Function Letter_Gap(A As String) As Double
Function Middle_Digits(A As String) As String
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Result of a User Defined
Function
 To specify the data type for the result
of a user defined function, place the
word “As” immediately after the last
closing parenthesis in the function
argument declaration followed by the
data type.
 The result of a user defined function
can be thought of as what the
function “outputs”.
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Result of a User Defined
Function (cont.)
 Examples:
Function F_To_C(F As Double) As Double
Function Perp_Bisector_Slope(x1 As Double, y1 As Double, x2 As Double, y2 As Double) As Double
Function Quadratic_1(A As Double, B As Double, C As Double) As Double
Function Letter_Gap(A As String) As Double
Function Middle_Digits(A As String) As String
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Local Variables
 A local variable is a variable declared within
a user defined function or sub-routine.
 Local variables can only be used in the user
defined function in which they are declared.
 When a user defined function or subroutine ends, the local variable no longer
exists, and Excel frees up the memory that
the local variable used.
 Local variables are often used to store
intermediate results and to do other
“chores”.
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Local Variables (cont.)
 Example:
Function Perp_Bisector_Intercept(x1 As Double, y1 As Double, x2 As Double, y2 As Double) As Double
'Returns the y-intercept of the line that is the "perpendicular bisector" of the line segment
'determined by points (x1,y1) and (x2,y2)
'The function does NOT work for vertical lines
Dim m As Double
Dim Midpoint_X As Double, Midpoint_Y As Double
‘blah
‘blah
‘blah
End Function
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Forcing Programmers To
Declare Variable Types
 It is considered good programming
practice to declare all variables.
 To enforce this, use the VBA “Option
Explicit” directive at the TOP of the
module before any function or subroutine declarations.
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Variable Assignment
 When dealing with assignment statements, VBA
always evaluates the expression on the righthand side of the equals sign and stores the result
in the variable on the left-hand side of the equals
sign.
 It is sometimes helpful for “beginning
programmers” to think of the equals sign as an
arrow pointing to the left.
 Some programming languages automatically
initialize variables to a default value (0, or the
null-string) while others do not.
 It is considered “good” programming practice to
ALWAYS initialize variables regardless of the
programming language used.
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Variable Assignment (cont.)
 Example 8:
What are the
values of J and K
before and after
each line of the
following VBA
code:
“VBA”
Value of J and
K
K = 4
K
4
K = K + 1
K
K+1
J = K
J
K
J = K+1
J
K+1
K = J
K
J
K = J+J
K
J+J
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Variable Assignment (cont.)
Value of J Before Value of K Before Line
Value of J After
Value of K After
?
?
K = 4
?
4
?
4
K = K+1
?
5
?
5
J = K
5
5
5
5
J = K+1
6
5
6
5
K = J
6
6
6
6
K = J+J
6
12
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How to “Return” the Result of a
User Defined Function
 Example:
Function Hello_World() As String
‘Return “Hello World!!!!”
Hello_World = “Hello World!!!!”
End Function
 Example:
Function F_To_C(F As Double) As Double
‘Return 5/9*(F-32)
F_To_C = 5/9*(F-32)
End Function
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How to “Return” the Result of a
User Defined Function (cont.)
 Example:
Function Slope(x1 As Double, y1 As Double, x2 As
Double, y2 As Double) As Double
‘Returns the slope of a line defined by the points
(x1,y1) and (x2,y2)
‘The function does NOT work for vertical lines
Dim m As Double
m = (y2-y1)/(x2-x1)
‘Return the value of m
Slope = m
End Function
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References
 VBA Excel Notes – John Albers
 Form Controls
 Overview: http://office.microsoft.com/en-us/excelhelp/overview-of-forms-form-controls-and-activexcontrols-on-a-worksheet-HA010237663.aspx?CTT=3
 List Box or Combo Box
http://office.microsoft.com/en-us/excel-help/add-alist-box-or-combo-box-to-a-worksheetHP010236681.aspx#BM1
 Scroll Bar or Spin Button
http://office.microsoft.com/en-us/excel-help/add-ascroll-bar-or-spin-button-to-a-worksheetHP010236682.aspx?CTT=1
 Shortcut Keys
 http://office.microsoft.com/en-us/excel-help/excelshortcut-and-function-keys-HP001111659.aspx
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