Working with Numeric Variables (Unit 6) Visual Basic for Applications.
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Transcript of Working with Numeric Variables (Unit 6) Visual Basic for Applications.
Working with Numeric Variables(Unit 6)
Visual Basic for Applications
Objectives
In this unit, you will learn how to:
Reserve a numeric variable
Perform calculations using arithmetic operators
Add a list box to an Excel worksheet
Use the Excel VLookup function in a procedure
Search a table in Word
Refer to the Access ADO object model in code
Use the Recordset Object’s Find method
Concept Lesson:Discussing numeric variables
Use Dim statements to reserve a procedure-level numeric variable, which is a memory cell that can store a number only
Variables assigned either the Integer or the Long data type can store integers, which are whole numbers
The differences between the two data types are in the range of numbers each type can store and the amount of memory each type needs to store the numbers
Open VBE and search for Data Type Summary
Data Types Used to Reserve Numeric Variables
Exhibit 6-1: The datatypes used to reserve numeric variables
Search for “Data Type Summary” in VBE help box
Reserving a Procedure-level Numeric Variable
The memory requirement of a data type is an important consideration when coding a procedure
Long data type uses 4 bytes of memory, while the Integer data type uses only 2 bytes
Exhibit 6-2: Some examples of Dim statements that reserve numeric variables
Assigning a Numeric Literal Constant to a Numeric Variable
A numeric literal constant is simply a number
A numeric literal constant cannot contain aletter, except for the letter E, which is used in exponential notation
Numeric literal constants cannot contain special symbols, such as the % sign, the $ sign, or the comma
They also cannot be enclosed in quotation marks (“”)
or number signs (#),
Assigning a Numeric Literal Constant to a Numeric Variable
Exhibit 6-3: Some examples of valid and invalid numeric literal constants
Exhibit 6-4: Some examples of assignment statements that assign numeric literal constants to variables
Assigning a Numeric Expression to a Numeric Variable
Numeric expressions can contain items such as numeric literal constants, variable names, functions, and arithmetic operators
The precedence numbers represent the order in which the arithmetic operations are processed in an expression
You can use parentheses to override the order of precedence because operations within parentheses always are performed before operations outside of parentheses
Assigning a Numeric Expression to a Numeric Variable
When you create a numeric expression that contains more than one arithmetic operator, keep in mind that VBA follows the same order of precedence as you do when evaluating the expression
Exhibit 6-5: The arithmetic operators and their order of precedence
Examples of Assignment Statements Containing Numeric Expressions
Exhibit 6-6: Some examples of assignment statements containing numeric expression
Summary
To reserve a procedure-level numeric variable:
Use the Dim statement. The syntax is Dim variablename As datatype
where variablename represents the name of the variable (memory cell)
and datatype is the type of data the variable can store
Variable names must begin with a letter and they can contain only letters, numbers, and the underscore
To assign a value to a numeric variable:
Use an assignment statement in the following syntax: variablename=value
Excel Lesson:Using numeric variables in Excel
Open Jake’s workbook and viewthe Paradise Electronics price list.
Creating a List Box
A list box is one of several objects, called controls, that can be added to a worksheet
You typically use a list box to display a set of choices from which the user can select only one
List boxes help prevent errors from occurring in the worksheet
To add a list box control to the worksheet, use the Control Toolbox toolbar
Inserting Controls You should enable Developer tab in Office 2007 to
insert Controls There are two types of controls:
Form Controls
ActiveX Controls
Form controls were the original controls and are much more simple
ActiveX controls offer more formatting properties MS does not include ActiveX controls for the Mac
Control Toolbox Toolbar(Search for Overview of Form Controls)
Exhibit 6-7: The Control Toolbox toolbar
Creating a List Box
To change the value assigned to several of the list box’s properties, use the Properties window
The Object box, located immediately below the Properties window’s title bar, displays the name and type of the selected object
Exhibit 6-8: The Properties window
Creating a List Box
The Properties list, which can be displayed either alphabetically or by category, has two columns
The right column, called the Settings box, displays the current value, or setting, of each of those properties
List Box Control Drawn on the Worksheet
Exhibit 6-9: The list box drawn on the worksheet
Coding the List Box’s DblClick Event Procedure
A list box’s DblClick event procedure occurs when the user double-clicks an item in the list
Exhibit 6-10: The pseudocode for the list box’s DblClick event procedure
Variables Used by the List Box’s DblClick Event Procedure
Exhibit 6-11: The variables used by the list box’s DblClick event procedure
Using the Excel VLookup Function in a Procedure
You can use the VLOOKUP function to search the first column of a range of cells, and then return a value from any cell on the same row of the range.
When range_lookup is True (default) the VLookup function performs a case-insensitive approximate search
stops when it reaches the largest value that is less than or equal to the lookup_value
Syntax of the VLookup Function
Exhibit 6-12: The syntax of the Vlookup function
Examples of theVLookup Function
Exhibit 6-13: Some examples of the Vlookup function
Word Lesson:Using numeric variables in Word
Open Pat’s document and view the UpdateMembership procedure.
Pseudocode for the UpdateMembership Macro
Exhibit 6-14: The pseudocode for the Updatemembership procedure
Variables Used by the UpdateMembership Procedure
Exhibit 6-15: The variables used by the UpdateMembership procedure
Searching a Table
In Word, you can search a column in a table first by selecting
the column, and then using the Execute method of the Find
object to locate the desired value
Moving the Insertion Point to the Beginning of the Document
You can use the Selection object’s HomeKey method to move the insertion point to a different area in the document
The HomeKey method, whose syntax is expression.HomeKey Unit:=unit, corresponds to the functionality of the Home key on your keyboard
In Microsoft Word, a story is defined as an area of a document that contains a range of text that is distinct from other areas of text in the document
Using numeric variables in AccessThe ADO Object Model
The ADO (ActiveX Data Objects) object model contains allof the objects needed to manage the records contained in one or more tables
Exhibit 6-16: A portion of the ADO object model showing the most commonly used ADO objects
The ADO Object Model
A Connection object represents the physical connection between an Access database and a data provider, which is a set of complex interfaces that allows ADO objects to use the data stored in a database
Immediately below the Connection object in the ADO object model is the Recordset object, which represents either all or a portion of the records (rows) contained in one or more tables
Coding the PaymentUpdate Procedure
Begin by opening this database and viewing the Payments table
Open Professor Martinez’s database and view the Payments table.
Pseudocode for the PaymentUpdate Procedure
Exhibit 6-17: The pseudocode for the PaymentUpdate procedure
Variables Used by the PaymentUpdate Procedure
Exhibit 6-18: The variables used by the PaymentUpdate procedure
Using the Recordset Object’s Open Method
You use the Recordset object’s Open method to open a recordset
The syntax of the Open method is recordset.open Source:=datasource, ActiveConnection:=connection, CursorType:= cursortype, LockType:=locktype, where recordset is the name of a Recordset object variable, datasource specifies the data source, and connection is the name of a Connection object variable
Valid Constants for the Open Method’s CursorType and LockType Arguments
Exhibit 6-19: The valid constants for CursorType and LockType arguments
Using the Recordset Object’s Open Method
The cursortype and locktype arguments in the syntax can be one of the constants
The LockType argument preventsmore than one user from editing a specific record at the same time by locking the record, making it unavailable to other users
Using the Recordset Object’s Find Method
You can use the Recordset Object’s Find method to search for a value contained in a field in the recordset
The syntax of the Find method is recordset.Find Criteria:=criteria
Examples of Using the Find Method to Search the rstPays Recordset
Exhibit 6-20: Some examples of using the Find method to search the rstPays recordset