Branching and Looping

1
Branching and Looping

• Managing Flow in a Script

2
Overview

• What is branching and looping
• if then
• while
• for each
• lists
• continue, break, return, exit
• In-class exercise next week

3
Wait- Before getting into this

• Ive got a really cool project for 3-5 people
• Engineering Application/Transportation Design --
  GIS for Preliminary Line
• Wed 3/21 -- 930 a.m. Bray 315 -- Scope out
  project with users
• Wed 4/11 -- 930 a.m. Bray 315 -- Progress report
• Wed 4/25 -- 930 a.m. Bray 315 -- Instruction
• Thurs. 4/26 -- 1 to 4 p.m. Moon 14 --
  Lab/Instruction

4
Also

• Paid Internship with CS Engineering here in
  Syracuse
• Email Abeer Khatib
• akhatib_at_cscos.com
• Map making (ArcView proficiency)
• Database (Access)
• Could be more..

5
Branching and Looping

• Branching statements use Boolean conditions to
  determine which set of code runs - if/then/else
• Looping statements commonly use collections
  (lists), or groups of objects to determine how
  many times a set of code is applied. Loops can
  also use a boolean condition to determine whether
  or not they loop and when to stop - while/for each

6
Why?

• To control flow of the program!
• You tell it what to do upon a certain condition
  being met
• Basic and essential in programming
• Dictates user interaction, when calculations are
  being made, what order to execute, etc

7
Conditional Branching

• If/Then statements use a condition to determine
  which part of the script executes. You can check
  a condition, and depending upon whether it is
  true or false, execute different lines of code.
• Must end with end
• Lets try it 1

8
Nesting?

• Basically an if/then statement within another
• or using elseif
• Lets try it -- 2

9
Boolean Expressions

• true, false
• could be returned value from expression
• myAttCond myTheme.HasAttributes
• Boolean expressions must be in parenthesis
• Compound expressions are done with boolean logic
  and, or, not, xor
• my Condition ((thePword lagis) and (theNum gt
  3))
• Lets try it 3

10
Loops - While

• Loops execute lines of code more than once based
  on the condition being met.
• We use while and for each
• A while statement loops through a set of requests
  as long as (while) the condition is true! When
  the condition changes to false, it stops.
• To make sure you dont hang-up, change the
  condition within the loop -- just in case!
• Must have end Lets try 4

11
Loops - For each

• The for each statement loops through each object
  in a collection and performs a set of requests.
  It initializes anObject to the first object in
  aCollection. The loop continues until the last
  object in the collection is read.
• Huh?
• Must also have end

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Loops

• In other words we can send the same set of
  requests to the objects in the list
• for each theObject in aCollection
• do something
• end
• Increments too!
• for each num in 0 .. 5 by 2
• do something
• end Lets try 5

13
Lists

• We will do more in following weeks, but...
• From the Collection Class
• A list is an ordered group, or collection of
  objects. A list can contain objects of different
  types.(strings, numbers, themes)
• Referenced by index number starting with 0 and up
  to n-1
• Make them with Make or myList x,y!
• Lets do 6

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Lists

• Get them with Get
• Populate them (put stuff in them) with Insert and
  Add
• Use Remove to delete an object from the list
• Count counts the number of objects in the list
• Find to return index number of an object
• FindbyValue for strings or numbers

15
List Issues/Number Issues!

• When counting or doing calculations,
• a lot of times we want to make sure to zero-out
  our variables so that previous memory does not
  get in our way .sum0 before adding numbers
• When using count in a list zero-out with -1

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Flow Control

• continue, break, return and exit
• continue skips the current iteration of the loop
  and goes to the next iteration
• break causes immediate exit from the loop you are
  in and goes to the next statement after the end
• return immediately terminates the current script
• exit terminates ALL running scripts
• Lets check out 7 to put it all together

17
For next week

• In-class exercise (1 of 3)
• Show us one of your modified scripts (bringing
  your disk)
• Demonstrate and explain what it does
• Display the script
• Everyone signed-up for credit will do one
  (thirds)
• next week ex5
• following ex6 and ex7
• when not presenting you all will assess the
  several presenters

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Ex5?