Irwin/McGraw-Hill Copyright© 2000 by the McGraw-Hill Companies, Inc. PowerPoint® Presentation to accompany prepared by James T. Perry University of San Diego

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Ch. 3:Variables, Constants, & Calculations  Data—Variables, Constants, & Controls  Data Types  Naming Conventions  Variable Scope  Calculations  Val function  Arithmetic Operations  Formatting Data  Programming Hints—Counting/Summing

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Data—Variables & Constants Data Types –Boolean, Byte, Currency –Date, Double, Integer, Long –Single, String, Variant intMaximumNumber = 100 intMaximumNumber 100

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Declaring Variables & Constants  Variables: Dim variable-name As data-type  Constants: Const constant-name As data-type = value  Most important: Force varibles to be explicitly declared: Select Tools, Options, Editor tab, and click the “Require Variable Declaration” check box.

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Naming Variables & Constants  Naming rules keep track of variable types  Naming rules help you remember which are constants and which are not  They avoid data conversion  Default data type is Variant  You can detect misspellings by typing variables in lowercase

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Naming Variables  All lowercase variables are converted to their “dimmed” spelling.  Attach prefix to the variable name: bln-Boolean, cur-currency, int-integer, sng-single precision, str-string  Examples: strSocialSecNum, intQuantity, intHoursWorked, curPayRate

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Constants—Named & Intrinsic  Using named constants follows conventional programming practice  Use named constants in lieu of “magic numbers” –increases documentation, –decreases likelihood of errors –facilitates global value changes –eases program maintenance

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill More about Constants  Examples of declaration: Const strRptName As string = “October Report” Const curTaxRate As Single =  Place constant declarations in lowest "covering level" you can.

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Intrinsic Constants  Intrinsic constants are system-defined constants  They use a two-character prefix to indicate the source –vb means Visual Basic –db means Data Access Objects –xl means Excel

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Scope of Variables  Scope is the availability of a variable –Global: can always be used or seen across the entire project –Module: accessible by all procedures in the form –Local: accessible only from single procedure in which it is declared –Static: local variables that are “remembered” across invocations of a routine but not outside it

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Scope of Variables (continued)  Code module-level declarations in General Declarations section of a form.  Code Local and Static variables in subprocedures.  Variable's lifetime is the period of time that the variable exists.

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Calculations & the Val Function  Standard Operators: (), ^, *, /, +, -  Operator precedence determines how an equation is evaluated  Example: curTotal = curTotal + curLatest  Val function converts Text to value; reduces errors for blank entries in text box  Counting occurrences: intSum = intSum + 1

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Formatting Data  Alter the displayed form of a number or string by formatting it  Special format functions exist to speed the process including FormatPercent  Form of a typical format function: FormatCurrency(NumericExpressionToFormat)  FormatCurrency(curTotalDue)

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Format Function Examples  lblTot.Caption = FormatCurrency(curTotal)  lblDate.Caption = FormatDateTime(intBirth)  lblQuantity.Caption = FormatNumber(intDone)  lblPercentDone.Caption = FormatPercent(txtDaysWork/txtTotalDays)

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Counting and Accumulating Sums  Counting: intCount = intCount + 1  Accumulating a sum: mintTotal = mintTotal + intNew  Averaging: msngAverage = mintTotalScore / intCount

Copyright© 2000 by the McGraw-Hill Companies, Inc.Irwin/McGraw-Hill Calculation Program Example summary information