Variables and Conditionals

1. Variables and Conditionals Hal Helms halhelms.com

2. What we'll cover • Basics of variables • Types of variables (strings, arrays, etc.) • Scopes of variables (session, application, etc.) • Conditionals (working with boolean variables)

3. Basics • Variables are name/value pairs • Variables permit our programs to work with values that can't be known at design time or that may change from their original value • customerName • yourStreetAddress • currentUser

4. Basics • Variables give context and constraint to values • The value "42" is meaningless apart from a context, usually provided by variable name (e.g. meaningOfLife) • Data typing constrains variables to hold meaningful values • isNumeric() returns a boolean value • randRange() returns an integer value

5. Strong data typing • Some languages employ strong typing, requiring the programmer to declare a variable's data type prior to using it • String myName; • int myAge; • Company myEmployer; • Examples • Java • C#

6. Weak data typing • Other languages use weak typing, in which the language implicitly determines the data type of a variable • Examples • Smalltalk • ColdFusion • Weakly typed languages are not untyped languages!

7. Data typing • Different data types hold different types of values • string • int • structure • Car "Visualize whirled peas" 1024 name "Hal Helms" ACMmember true numberOfChildren 1

8. ColdFusion data types • string • numeric • query • list (string) • structure • array • object • boolean • date • GUID • UUID

9. Complex variable type: query • query • series of 1 or more rows with column or field values for each row id price description 100 29.99 Widget 200 75.00 Framus, left-handed products • addressable • products.price — refers to current row • products.price[2] — specifies row

10. Complex variable type: structure • structure • collection of name/value pairs grouped around a central idea or item teacher Hal Helms Ben Edwards maxStudents 10 isActive true javaClass • addressable • javaClass.maxStudents • javaClass['maxStudents']

11. Complex variable type: 1-d array • one-dimensional array • collection of ordered values • resembles a single row of a spreadsheet [1] [2] [3] Ben Edwards Hal Helms Sean Corfield onedee • addressable • onedee[2]

12. Complex variable type: 2-d array • two-dimensional array • collection of ordered values • resembles multiple rows of a spreadsheet [1] [2] [3] [1] 72 68 84 69 62 69 [2] • addressable • twodee[1][3] twodee

13. Complex variable type: object • Objects are fundamentally different from all other data types in that they encapsulate both data and behavior • Objects allow us to create scale models of the world under consideration • Car • getMake(): string • addGas(gallons): void • accelerate(): void

14. Quiz time! • For each of the following,explain which data type you'd use and why • final test scores for all students • collection of Student objects • lyrics to "Memories" (thank heavens for garbage collection!) • number of students in a class • information from LDAP server • composer's date born, date died, nationality, typical genre • an hourly employee

15. Understanding scopes • A variable typically has a lifespan and a scope • lifespan: how long the system keeps a reference to a variable • scope: location from which variable is visible • In ColdFusion, a variable's scope and lifespan are bound together in a single attribute, scope, which is prefixed to the variable name

16. Understanding scopes

17. Quiz time! • For each of the following,explain which scope you'd use and why • global "constants" such as datasource name • query meant to be created and used on same page • a CFC, currentUser, that encapsulates data and behavior for the currently logged in user • a cookie crumb array • a userID meant to identify the user between visits • a custom tag "reaching into" the base template to read or set a variable on that page

18. Conditionals • All conditionals involve carrying out some instructions based on whether an expression evaluates to true

19. <cfif> <cfif form.betNumber EQ winningNumber> <cflocation url="index.cfm?fuseaction=home.winner" /> </cfif>

20. <cfelse> <cfif form.betNumber EQ winningNumber> <cflocation url="index.cfm?fuseaction=home.winner" /> <cfelse> <cflocation url="index.cfm?fuseaction=home.loser" /> </cfif>

21. <cfelseif> <cfif form.betNumber EQ winningNumber> <cflocation url="index.cfm?fuseaction=home.winner" /> <cfelseif form.betNumber LT 0> <cflocation url="index.cfm?fuseaction=home.cheater" /> <cfelse> <cflocation url="index.cfm?fuseaction=home.loser" /> </cfif>

22. iif() <cfset randomBoolean = iif(RandRange(0,1), true, false) />

23. switch/case <cfswitch expression="#attributes.fuseaction#"> <cfcase value="home"> <cfinclude template="dspHome.cfm" /> </cfcase> <cfdefaultcase> <cfinclude template="qryMenuItems.cfm" /> <cfinclude template="dspMenu.cfm" /> </cfdefaultcase> </cfswitch>

24. Conclusion • Variables are the basis of all programs • Data typing, although mostly hidden in ColdFusion, is very important—particularly in OO languages • Do experiment with "complex" data types; you'll find they make your code easier to write and maintain • Conditionals allow us to execute commands based on the result of some run time boolean value