visual basic objects / properties / methods propertyadjective objectnoun part of the application...

Visual Basic

Objects / Properties / Methods

Property Adjective

Object Noun Part of the application

Attribute

Method Verb Action to dosomething

Visual Basic

Range (“A3”).select

Range is an object

select is a method

(“A3”) is a modifier for the object

Note that object separated from method by a .

Activesheet.name

Activesheet is an object

name is a property

Visual Basic

The result is the name of the active sheet

Procedures

Sub procedures return no values except by changes to parameters in the argument list

Function procedures return a value by assigning itto the name of the function.

Function Procedures

Function Grade (exam1,exam2,exam3) as String

Sum = exam1+exam2+exam3If Sum > 95 then Grade = “A”Elseif Sum > 80 Grade = “B”Else Grade = “C”Endif End Function

Dim Sum as Single

For functions and sub procedures, there is a one to one correspondence between the arguments in the call to the function and the argument list of the function:

Function Grade (exam1,exam2,exam3) as String

The call:= Grade( 90, C40, $C$60 )

The definition:

Sub Procedures

Public Sub ColorList()' Lists all the available colors in the current pallette' Number is listed in column 2, color sample in column 3' List starts in row 5Dim I As IntegerDim J As IntegerDim K As IntegerJ = 5I = 2For K = 1 To 56 Cells(J, I).Value = K Cells(J, I + 1).Interior.ColorIndex = K J = J + 1Next KEnd Sub

Note that ColorList is never assigned a value!

Review of some Excel Basics

Cell references of two types:

A1 Columns are alphabetic, rows are numeric

R1C1 R number Column number

B2 and R2C2 refer to the same cell

Can be set by the Tools / Options menus

(Note that the two methods are transposed –A1 – column first, then row R1C1 – row first, then column )

Formulae in Excel (R1C1 style)

R1C1 is an absolute address – it does not change under copy / paste

R[1]C[1] is a relative address – it does change under copy /paste

And can use mixed mode:

R1C[1] – R1 is absolute, C[1] is relative

In VBA, can use either or both A1 and R1C1 styles

A1 style tends to be absolute

A1 style used with the “Range” objectRange(“A4”)

Can refer to individual cells with the “Cells” object, which uses an R1C1 styleCells(4,1)

In Excel, cells & ranges can be namedInsert / name menu

These names can be used in FormulaeVBA

VBA Variable Types

String A sequence of bytes containing charactersInteger 2 byte integerLong 4 byte integerSingle 4 byte real numberDouble 8 byte real numberVariant Can hold anything (but “expensive” to use)“Object” A class of data types used by Excel/VBA

Characters & Stings

For Excel, anything that is not a number or a formula is a string. If want a set of digits as a string, need to enclose in quote or quotation marks.

For VBA, need to define variable that will hold strings as string data types

Visual Basic

Sub NameIt()Dim newname as Stringnewname = InputBox(“Enter a name for the worksheet”)ActiveSheet.Name=newnameEnd Sub

Example -- simple Sub to name the active worksheet:

“Object” data type

Many of the objects in Excel have their owndata type:

Dim r as RangeDim q as WorksheetDim z as Chart

About the only one we will use is the “Range”data type.

Option Explicit

Forces you to ‘Dim’ all variables

Helps prevent typos

Can set this as the default through the Tools/ Options menu.(Require variable declaration check box)

Visual Basic

All objects have properties

Most objects have methods

Will work with only a few of the many objects, methods and properties

To get a list of objects and properties, invoke the Object Browser (F2)

Program module (Sub or Function) is made up of a series of steps to accomplish a task. Five major categories of steps:

Assignment statements A = 5

Conditional statements If ( A > 5) then ….

Calls to other modules A = sqrt (12)

Input /Output operations(Which are really calls to other modules)

Read 5, A

Iteration Statements For I = 1 to 6 … Next i

Expression evaluation inVBA

Operators in priority orderLeft to right

Operator Priority List ( )^- (unary minus)* /+ -

Comparison Operators (>, < …)

Logical Operators (NOT, AND, OR…)

Test = 2 + 3 ^2 > 5 AND (3-7)*2 > 6

(3-7) -43^2 9-4*2 -89+2 1111 > 5 True-8 > 6 FalseTrue AND False False

Thus, Test has the value “False”

Conditional Expressions

If / then / else end if

Select case …. End Case

If (expression) then

One or more expressions

Else

One or more expressions

End If

If (expression ) then (expression)

Note: no End If statement for this type of If /then expression

Select Case testexpression[Case expressionlist-n[statements-n]] ...

[Case Else[elsestatements] ]

End Select

Select Case Statement

Like a complex If / Then / ElseIf … / EndIf

Select Case Statement

Testexpression can be any that evaluates to a numeric value or a string

Expressionlist is compared to the testexpression to determine if the following statements should beexecuted. See “Help” for all the allowable forms

Statements are executed up to the next Case statement or the End Select statement

A simple example

Case statements to determine a letter grade from a numeric grade. Assume the numeric grade is in the variable “grade”

Select Case gradeCase Is >=90

ltrgrade=“A”Case Is >= 85

ltrgrade = “BA”…Case Is >= 70

ltrgrade = “C”Case Else

ltrgrade=“E”End Select

Note: Goes to first Case that testexpression satisfies. Is implicitly uses grade in the comparison

Generally speaking, anything you can do with a Select Case block, you can do with a set of If / Then / Else If … / End If statements

Iteration Statements Used to execute a number of statements

repeatedly

Two major types ---For / Next Do / Loop

For counter to upperlimt step sizeStatements

Next counter

For Each cell In Selection Statements

cell.value= expression

Next cell

Dostatements

Loop

Basic “ Do Loop” Structure

But we need a mechanism to stop the loop!

Do while expression_is_true StatementsLoop

Do Statements

Loop while expression_is_true

Do Until expression_is_true StatementsLoop

Do Statements

Loop Until expression_is_true

Do...Loop Statement ExampleThis example shows how Do...Loop statements can be used. The inner Do...Loop statement loops 10 times, sets the value of the flag to False, and exits prematurely using the Exit Do statementThe outer loop exits immediately upon checking the value of the flag.

Dim Check, Counter Check = True Counter = 0 ' Initialize variables. Do ' Outer loop.

Do While Counter < 20 ' Inner loop. Counter = Counter + 1 ' Increment Counter. If Counter = 10 Then ' If condition is True.

Check = False ' Set value of flag to False. Exit Do ' Exit inner loop.

End If Loop Loop Until Check = False ' Exit outer loop immediately

To manipulate a cell’s value, use the “value” property of the cell object:

Range(“A4”).value = 20Temp = Range(“A4”).value

orCells(4,5).value = 20Temp = Cells(4,5).value

Build a simple module to set a 5 x 5 array of cells to some value

In VBA IDEInsert moduleInsert procedure / sub

Initcells

Dim I as integerDim J as integerFor I = 1 to 5For J = 1 to 5Cells(I,J) = I*JNext JNext I

Return to Excel and run macro Initcells

Two useful VBA functions to interact with use:

Str1 = InputBox(“prompt’)

When invoked, displays the prompt and gives you a box to enter a reply, which is placed in Str1

Dim str1 as Stringstr1 = InputBox(“Please enter your name”)

InputBox displays a prompt and awaits a reply

MsgBox displays a message and buttons to press. The function value returned is the code for the button

J = MsgBox(“prompt”,buttoncodes, “ box name”)

Look at ‘Help” for the button code valuesJ is the integer value of the button code the user presses

Code=MsgBox(“Are you OK”,vbOKOnly,”My Temp”)

Write a simple sub (called Heater) that accepts a temperature as an argument and returns a string to indicate what to do with the heater. Also have MsgBox display a message to the use if the heater status is changed.

The logic for the heater control is as follows:

If the temperature is less than 65, “Turn heater on”If the temperature is greater than75, “Turn heater off”Otherwise, “Leave heater alone”

Function Heater (Temp) As stringCode

End function