CIS 451: ASP.NET Concepts

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CIS 451 ASP.NET Concepts

• Dr. Ralph D. Westfall
• January, 2009

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Former Visual Basic Family

• Visual Basic
• standalone development product
• VB for Applications
• subset of VB
• works within Microsoft applications
• VBScript
• subset of VBA, for Internet applications

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Previous VBScript

• "chopped down" version of Visual Basic
• many of same
• data types
• syntax
• control structures
• functions

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ASP.NET Is Not Just VB

• can also use C, C, C, J, JScript.NET, Perl,
  and other languages
• just as CGI can work with different languages
• ASP.NET supports more than 25 languages
• additional languages expected to be adapted to
  work with .NET in the future

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VBScript Data Types

• all VBScript data stored as variants
• can't declare with types as in VB
• actual type based on data assigned to variable
• can subsequently use a different type
• Dim varLength
• varLength 5
• varLength "five"

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ASP.NET Data Types

• 11 primitive types built into .NET framework
• 4 integer types Byte, Short, Integer, Long
• 3 decimal types Single, Double, Decimal
• Text String and Char (Char is really a )
• Other Date and Boolean
• objects are also a data type
• but not a primitive type

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Variable Naming Conventions

• in some programming languages, people like to
  attach the data type to the front of the variable
  name
• also known as "Hungarian notation"
• popular at Microsoft
• not popular with Java programmers
• cultural issue between Microsoft and rest of
  world?
• bottom line Prof. Westfall likes for objects

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Object Naming Convention

• btn Button
• cbo Combobox
• chk Checkbox
• dg Data grid
• frm Form
• gpb Group box
• img Image
• lbl Label

• lst Listbox
• mnu Menu
• opt Option button
• (Radio button)
• pic Picture
• rpt Report control
• txt Text Box

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Object Naming Issues

• advantages of a convention
• makes code easier to debug and maintain
• improves your grade on projects
• disadvantages of a convention
• 1-letter declarations dont always match
• Dim sName as string
• Dim fSmallDecimal as Single
• extra work

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Other Variable Naming Issues

• all variable names must start with a letter
• use letters and numbers
• avoid other (special) characters (other than
  underscore _ )
• capitalize initial letters of words after
  prefixes
• datQuarterStarts
• datQuarterEnds
• use meaningful names of reasonable length

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Other Data Types

• object
• can have multiple values of different types
• empty memory location but no value
• NULL no data at all
• nothing (not even 0 or blank or "")
• has no memory location
• error

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Declaring Variables

• implicit (ASP.NET figures out type)
• Dim strCustName "Lee" 'string
• only works if StrictFalse (next slide)
• explicit (better)
• Dim strCustName as String
• strCustName "Lee"
• 'OR
• Dim strCustName as String"Lee"

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Setting Declaration Options

• to force declaring all variables and to avoid
  type conversion errors
• lt_at_ Page Language"VB" StrictTrue gt
• put on very first line of file of ASP file
• could use ExplicitTrue instead
• allows implicit declarations e.g.,
• Dim strCustName"Li" 'no as Type

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Array Variables

• Dim strUSAStates(49)
• strUSAStates(0) "AL"
• counts from 0 (same as in C, etc.)
• Redim Preserve strUSAStates(50)
• changes size without losing current data
• Dim strTicTacToe(2,2)
• for a 3 x 3 array

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Constant

• value can't change
• naming convention is to capitalize all letters in
  name
• makes code more understandable
• Const TAX_RATE .28
• UNDERSCORES_SEPARATE_WORDS
• in contrast to "camel case" coding

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Variable Scope

• procedure level (local i.e., inside a Sub)
  variable values are NOT available elsewhere in
  ASP.NET code
• other variables (global level, outside of any
  Subs) are accessible to all ASP.NET code in a
  page (all Subs, and in HTML)
• 'see notes

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Subprocedures

• Sub ProcName(arg1 as Type, etc.)
• 'lines of code, including arg1
• ' other local/global variables
• End Sub
• Call ProcName(arg1, etc.)

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Operators

• assignment e.g., CustAge 22
• , -, , / (arithmetic)
• exponentiation e.g.,
• RSquare Radius2
• how does Java do exponentiation?

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Operators - 2

• \ operator for integer division (contra / )
• 7 / 4 1.75
• \ gives integer part 7 \ 4 1
• decimals are rounded off before integer division
• MOD gives remainder 7 MOD 4 3
• "clock arithmetic"

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Concatenation Operation

• link together in series or chain (Webster)
• concatenates items regardless of type
• "Le " "Dinh" "Le Dinh"
• 1 1 "11"
• concatenates strings like does, but
• 1 "1" 2 'except when StrictOn

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Concatenation - 2

• concatenation can construct ASP.NET code also
  (not just for calculations)
• intIndex 2
• Session("intProdQuantity" _ intIndex)
• evaluates to
• Session("intProdQuantity2")
• buya.aspx

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Comparison Operators

• (equal how does Java do this?)
• lt gt (not equal Java?)
• lt (less than)
• gt (greater than)
• lt (less than or equal)
• gt (greater than or equal)

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Logical Operators

• AND (Java?)
• OR
• NOT
• If nAge gt 65 AND strLocal TRUE Then

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String Handling Functions, Etc.

• strText.ToLower(), "abc".ToUpper()
• (converts to capitals or lower case)
• Len(strText) (or strText.Length)
• Left(strText, intN), Right(strTxt, intN)
• (returns intN left or right characters)
• Mid(strText, intWhere, intN)
• (intN characters, starting at intWhere)
• Excel demo

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String Handling - 2

• strText.IndexOf(StrFind, intStart)
• strText.IndexOf("some text")
• (finds location actual numeric position of
  StrFind variable or text within a String variable
  or literal starting at intStart)
• example check e-mail address format
• intLoc strText.IndexOf ("_at_", 2)
• (if returns value lt1, string wasn't found)

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String Handling - 3

• strText " abc "
• strText.TrimStart()
• "abc ".TrimEnd()
• remove spaces from left or right side
• strText.Trim()
• remove spaces from both sides

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Converting Variable Types

• strType TypeName(intWeight)
• (returns data type)
• intTons CInt(dblTons)
• strPop CStr(lngPopulation)
• (convert variables to Integer, String, etc.)

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Checking Types, Etc.

• IsNumeric(Request.QueryString("Zip"))
• checks to see if data is numeric
• IsDate(Request.QueryString("DoB"))
• checks to see if data is in a date format
• If Request.QueryString("CustName") "" Then
• If Request.QueryString("Zip") Is Nothing Then
• checks for missing data

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Line Continuations

• problem many VB.NET functions won't work if
  split onto more than 1 line
• solution use _ (space underscore) just before
  line break
• If Request.Form("CustEMail").IndexOf("_at_") _ gt 2
  AND _
• Request.Form("CustEMail").IndexOf(".") _
• gt 4 Then

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web.config Shows Code Errors

• Visual Studio.NET creates with project
• lt!-- Web.Config Configuration File --gt
• ltconfigurationgt
• ltsystem.webgt
• ltcustomErrors mode"Off"/gt
• lt/system.webgt
• lt/configurationgt