Excel 2019 Power Programming with VBA. Michael Alexander

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СКАЧАТЬ the faster the processing time. Another way to improve the speed of your code is by using the With-End With construct, which also reduces the number of dots to be processed. We discuss this construct later in this chapter.

The true value of object variables will become apparent when we discuss looping later in this chapter.

User-Defined Data Types

      VBA lets you create custom, or user-defined, data types. A user-defined data type can ease your work with some types of data. For example, if your application deals with customer information, you may want to create a user-defined data type named CustomerInfo.

      Type CustomerInfo Company As String Contact As String RegionCode As Long Sales As Double End Type

      NOTE

      You define custom data types at the top of your module, before any procedures.

      After you create a user-defined data type, you use a Dim statement to declare a variable as that type. Usually, you define an array. Here's an example:

      Dim Customers(1 To 100) As CustomerInfo

      Each of the 100 elements in this array consists of four components (as specified by the user-defined data type, CustomerInfo). You can refer to a particular component of the record as follows:

      Customers(1).Company = "Acme Tools" Customers(1).Contact = "Tim Robertson" Customers(1).RegionCode = 3 Customers(1).Sales = 150674.98

You can also work with an element in the array as a whole. For example, to copy the information from Customers(1) to Customers(2), use this instruction:

      Customers(2) = Customers(1)

      The preceding example is equivalent to the following instruction block:

      Customers(2).Company = Customers(1).Company Customers(2).Contact = Customers(1).Contact Customers(2).RegionCode = Customers(1).RegionCode Customers(2).Sales = Customers(1).Sales

Built-in Functions

Like most programming languages, VBA has a variety of built-in functions that simplify calculations and operations. Many VBA functions are similar (or identical) to Excel worksheet functions. For example, the VBA function UCase, which converts a string argument to uppercase, is equivalent to the Excel worksheet function UPPER.

      

Appendix A contains a complete list of VBA functions, with a brief description of each. All are thoroughly described in the VBA Help system.

      TIP

To get a list of VBA functions while you're writing your code, type VBA followed by a period (.).V BE displays a list of all its members, including functions (see Figure 3.3). The functions are preceded by a green icon. If this technique doesn't work for you, make sure that the Auto List Members option is selected. Choose Tools ➪ Options and then click the Editor tab.

FIGURE 3.3 Displaying a list of VBA functions in VBE

      You use functions in VBA expressions in much the same way that you use functions in worksheet formulas. Here's a simple procedure that calculates the square root of a variable (using the VBA Sqr function), stores the result in another variable, and then displays the result:

      Sub ShowRoot() Dim MyValue As Double Dim SquareRoot As Double MyValue = 25 SquareRoot = Sqr(MyValue) MsgBox SquareRoot End Sub

      The VBA Sqr function is equivalent to the Excel SQRT worksheet function.

      You can use many (but not all) of Excel's worksheet functions in your VBA code. The WorksheetFunction object, which is contained in the Application object, holds all the worksheet functions that you can call from your VBA procedures.

      To use a worksheet function in a VBA statement, just precede the function name with this:

      Application.WorksheetFunction

      The following example demonstrates how to use an Excel worksheet function in a VBA procedure. Excel's infrequently used ROMAN function converts a decimal number into a Roman numeral.

      Sub ShowRoman() Dim DecValue As Long Dim RomanValue As String DecValue = 1939 RomanValue = Application.WorksheetFunction.Roman(DecValue) MsgBox RomanValue End Sub

      When you execute this procedure, the MsgBox function displays the string MCMXXXIX.

      Keep in mind that you can't use worksheet functions that have an equivalent VBA function. For example, VBA can't access the Excel SQRT worksheet function because VBA has its own version of that function, Sqr. Therefore, the following statement generates an error:

      MsgBox Application.WorksheetFunction.Sqrt(123) 'error

      

In Chapter 5, you will discover that you can use VBA to create custom worksheet functions that work just like Excel's built-in worksheet functions.

      The MsgBox function

      The MsgBox function is one of the most useful VBA functions. Many of the examples in this chapter use this function to display the value of a variable.

      This function often is a good substitute for a simple custom dialog box. It's also a useful debugging tool because you can insert MsgBox functions at any time to pause your code and display the result of a calculation or an assignment.

      Most functions return a single value, which you assign to a variable. The MsgBox function not only returns a value but also displays a dialog box to which the user can respond. The value returned by the MsgBox function represents the user's response to the dialog box. You can use the MsgBox function even when you have no interest in the user's response but want to take advantage of the message display.

      The official syntax of the MsgBox function has five arguments (those in square brackets are optional).

      MsgBox(prompt[, buttons][, title][, helpfile, context])

       prompt: Required. The message displayed in the pop-up display.

       buttons: Optional. A value that specifies which buttons and which icons, if any, appear in the message box. Use built-in constants—for example, vbYesNo.

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