Use UPPERCASE to de ne constants in VB.NET

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C programmers have used this convention successfully for many years It pays to be able to pick out constants from other identi ers, since otherwise you might be tempted to try to assign values to them Refer back to the RETIREMENT_AGE code fragment for an example
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Documentation
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Program code is the culmination of the development life-cycle, of which the only other evidence that exists is the documentation speci cations, diagrams, etc As you will probably have noticed throughout this book, program code can be expressive, but still tells only part of the story While a subroutine can be written in a style that spells out quite clearly what is happening, there are other aspects that go beyond the code: the assumptions that have been made, the conditions under which the code can be expected to run (and fail), the place a piece of code has in the grand scheme of things
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Appendices
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To make a piece of code tell the whole story, extra documentation is necessary Within a program, this comes in the form of comments
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What Comments are used for
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Comments in program code play several distinct roles: 1 to state the purpose of a class or routine in plain words; 2 to describe the conditions required for a routine to run properly; 3 to indicate the effects that a procedure will have on variables and objects within its scope; 4 to state any known limitations of a piece of code; 5 to describe signi cant changes that have been made to program code; 6 to indicate who has written a module or procedure and when
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Styles of Comment
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I tend to use three forms of comment in test and production code These are:
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in-line comments, placed at the end of statements to further describe their purpose; single-line comments, normally placed immediately before a statement or block of code I wish to clarify; block comments, normally placed at the start of a module, before blocks of variable declarations, at the start of a procedure (sub, function or property) and in front of any passage of code that I think needs signi cant clari cation
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In-line comments are placed at the end of a line to explain it:
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Private Sub mnuFileSave_Click(ByVal sender As SystemObject, _ ByVal e As SystemEventArgs) _ Handles mnuFileSaveClick If fileName = "" Then 'fileName is a module variable FileSaveAs() 'Save the file with a new name Else FileSave() 'Save the file with the existing name End If End Sub
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Single line comments are used to describe the following section of code:
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'Then write out each Student For Each S In StudentsValues SWriteXML(writer) Next
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Appendices
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Block Comments are used to provide a heading for a signi cant structural item, a class, Sub, Function or Property:
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'In 'If 'of Sub this sub, we check whether a file exists it does, the file is loaded as a block text into txtFileInfo LoadText() Dim fileName As String Dim inStream As IOStreamReader fileName = "c:\data\TextFiletxt"
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Commenting out blocks of code
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You can temporarily remove a block of Visual Basic code from a program by commenting it out preceding each statement with a comment character (apostrophe) You can either do this laboriously a line at a time, or use the Comment Block command, available only from the Edit toolbar (select View/Toolbars and check the Edit toolbar) Select the text you want to temporarily disable and press the Comment Block button (hover the mouse pointer over buttons to see their names) All of the selected lines will be preceded with a comment character To remove the comments and restore the code, select the commented out lines and press the Uncomment Block button
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General Commenting Principles
Use comments to spell out your intentions Describe your intentions for a procedure in comments, and then ll in the program code, leaving the comments in place For example:
Sub LoadText(ByRef T As TextBox) 'Get the file name from an OpenFile dialog box 'Open the file and read the contents 'Close the file and transfer the contents to the text box 'If something goes wrong, report it End Sub
Now that the required process has been adequately described, it is a simple matter to ll-in the blanks and create the sub, either immediately or at a later date:
Sub LoadText(ByRef T As TextBox) Dim dlgOpen As OpenFileDialog = New OpenFileDialog() 'Get the file name from an OpenFile dialog box dlgOpenFilter = "Text Files | *txt | All Files | **" dlgOpenInitialDirectory = ApplicationExecutablePath If dlgOpenShowDialog = DialogResultOK Then fileName = dlgOpenFileName