INT213 – WEEK 1 ASP tags and comments Variables, Constants, and "Literals" Simple Output

ASP files and tags  Internet Information Services Microsoft web server Special processing for any URL ending in.ASP ASP files mix objects, VBscript and HTML are ASP tags  contain VBscript programming and ASP object commands

Variables  What is a Variable? A named storage location is assigned a value The value can change during the run of the script

Variables — Rules  Naming Rules begin with a letter, then letters or numbers no punctuation except _ underscore cannot be a VBScript command word  Recommendations for naming Variables declare all variables at the top of your file do not use numbers: what is date1 vs. date2? use descriptive terms: counter, name, price capitalize multiple words (camelCase): errorCounter, familyName, unitPriceDiscount

Literals  Literals are hard-coded values that do not change.  "ABC DEF" is a text or character literal Always enclosed in double quotes  123 is a numeric literal Never enclosed in double quotes  Usually used once in a script

Constants  are variables that do not change  contain literals used more than once  ' define constants Const PI = ' pi Const BR = " " ' HTML break  Naming rules are same as for Variables  Use all capitals for good style and _ to separate words: SCHOOL_NAME = "School of ICT"

Comments  ' from single quote to end of line ' area of a circle circleArea = PI * radius * radius  How many comments are enough? If your script contained ONLY comments and non-programmer understands it and a programmer could write the code then you have enough comments

Variables NOT Declaring variables - By default, you do not have to declare variables - Logic Errors occur when variables are mystiped e.g. <% count = 1' variable we meant Response.write counter' variable we typed %> - Nothing will be seen on the browser - counter contains the default empty value

Variables Declaring variable names Tell VBScript to spell check variable names. - forces declaration of all variable names - to dimension (declare) a variable name

Variables Declaring and using variable names <% Option Explicit  must be 1 st line of VBscript code Dim givenName, familyName givenName = "Scott" familyName = "Mitchell" %> Author familyNane is not a declared variable. ASP server will send error message: Microsoft VBScript runtime (0x800A01F4) Variable is undefined: 'familyNane' /Week1_Variable_demo.asp, line nn

Actual Data Types  see Day 3 of textbook re Data Types  Integer (numbers), String (text), Boolean (true/false), Currency, Date  Understand the difference between data types: Integer 12 is not the same as String "12" sum = ' sum is 3468 department = "12" product = "3456" sku = department + product ' sku is "123456"

Variables  Use at the top of.asp files to prevent VBscript variable naming errors.  variables have default value of empty meaning default values of "" (zero length string) when system expects text 0 (numeric zero) in most—but not all—numeric contexts.  It is best to assign a zero value to variables used as numbers at the top of the script.

Variables – whose are they? ‘SCOPE’ of a Variable  How far does it go?  How long does it last?  Three levels: 1.Page (.asp file) 2.Session 3.Application

Variables – whose are they? Page is everything in an.asp file lasts while the.asp file is processed global  variables declared at top of page  accessed by all VBScript within the page local  variables declared and accessed only within a function or subroutine

Variables – whose are they? Session is a single client using a site's pages within a length of time session variable cannot be declared is an ASP object accessed by VBScript using it: Session("varName") = … accessed by all VBScript in ALL pages in the Application (in the same folder) lasts until client session 'times out' maintained separately for each client by ASP: unique value for each client

Variables – whose are they?

Variables with values