CIS 451: ASP.NET Concepts

Dr. Ralph D. WestfallJanuary, 2009

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

Previous VBScript "chopped down" version of Visual

Basic many of same

data types syntax control structures functions

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

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"

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

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

Object Naming Conventionbtn Button

cbo Comboboxchk Checkboxdg Data grid frm Formgpb Group boximg Imagelbl Label

lst Listboxmnu Menuopt Option button (Radio button) pic Picturerpt Report control txt Text Box

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 don’t always match

Dim sName as stringDim fSmallDecimal as Single

extra work

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

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

Declaring Variables implicit (ASP.NET figures out type)

Dim strCustName = "Lee" 'string only works if Strict=False (next

slide) explicit (better)

Dim strCustName as String strCustName = "Lee" 'OR Dim strCustName as String="Lee"

Setting Declaration Options to force declaring all variables and

to avoid type conversion errors <%@ Page Language="VB" Strict=True %>

put on very first line of file of ASP file could use Explicit=True instead

allows implicit declarations e.g., Dim strCustName="Li" 'no as Type

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

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

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

Subprocedures Sub ProcName([arg1 as Type, etc.])

'lines of code, including arg1 '& other local/global variables End Sub

Call ProcName([arg1, etc.])

Operators = assignment e.g., CustAge = 22 +, -, *, / (arithmetic) ^ exponentiation e.g., RSquare = Radius^2 how does Java do exponentiation?

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"

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 Strict=On

Concatenation - 2 concatenation can construct

ASP.NET code also (not just for calculations) intIndex = 2 Session("intProdQuantity" & _ intIndex)

evaluates to Session("intProdQuantity2") buya.aspx

Comparison Operators = (equal [how does Java do

this?]) < > (not equal [Java?]) < (less than) > (greater than) <= (less than or equal) >= (greater than or equal)

Logical Operators AND ([Java?]) OR NOT

If nAge > 65 AND strLocal = TRUE Then

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

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 ("@", 2) (if returns value <1, string wasn't found)

String Handling - 3 strText = " abc " strText.TrimStart() "abc ".TrimEnd() remove spaces from left or right

side

strText.Trim() remove spaces from both sides

Converting Variable Types strType = TypeName(intWeight) (returns data type)

intTons = CInt(dblTons) strPop = CStr(lngPopulation) (convert variables to Integer,

String, etc.)

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

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("@") _ >= 2 AND _

Request.Form("CustEMail").IndexOf(".") _ >= 4 Then

web.config Shows Code Errors Visual Studio.NET creates with project<!-- Web.Config Configuration File --><configuration> <system.web> <customErrors mode="Off"/> </system.web></configuration>