Decision Structures Chapter 4 Part 2

Chapter 4 Objectives To understand o What relational operators are and how they are used o Boolean logic o Testing the value of an object’s property 4-2

Relational Comparisons  Relational Operators are used to compare values and determine whether relationships exist o Greater than o Less than o Equal to  Compare two values and determine how they relate to each other OperatorMeaning = Equal to ! =Not equal to >Greater than > =Greater than or equal to <Less than < =Less than or equal to 4-3

Relational Operators  Used to write your own comparison o In If/Else and other tests  Operates on two pieces of data o a and b  Alice uses “a” and “b” for placeholders o Drag the desired tile and replace either the “a” or “b” with a value 4-4

Concept Illustrated Relational operations are defined using relational operators 4-5

Boolean Logic Can check for multiple conditions at one time with Boolean logic instead of nesting If/else statements Boolean logic operators are used to build an expression composed of multiple conditions o And  Boolean: A and B: True only when both are true  In Alice: Both A and B o Or  Boolean: A or B: True when one or both are true  In Alice: Either A or B, or both o Not  Inverses what is sent to it Example: if A = True then not A is False  In Alice: not A 4-6

Boolean Logic in Functions Choose World object Then choose functions o Select desired Boolean function o Drag to conditional instruction like If/Else Condition 4-7

Logical Operators Tests more than true/false Can do complex testing Test two conditions to see if o They BOTH are true (and) o ONLY one condition is true (or) o NEITHER condition is true (not) 4-8

Example Can combine multiple conditions Example: Condition is true if o The penguin is within 2 meters o And the circle is wider than the penguin Similar to nested If/Else but doesn’t do contents of second Else statement o Penquin says “Drats“ 4-9

Testing Value of Object’s Property Sometimes you might want to see what a property of an object is o Color o Opacity o isShowing 4-10

How to Testing Object’s Property Create an empty If/Else instruction Select object to test Click properties tab Drag desired property’s tile and drop onto If/Else instruction’s condition Menu appears showing all comparisons to perform o Select desired comparison Another menu appears allowing you to select value that you want to compare property to o Ex: color property will give list of colors 4-11

Example Algorithm Frog and ladybug are in garden 4-12 Ladybug says “Excuse me” Frog turns to face ladybug If ladybug’s color is red Frog says “EEK! Go away!” Else Frog says “Good Morning” Endif

Property Test Demonstration 4-13

Homework Read chapter 4.4 Do lab assignments Answer questions in handout Due one week after assigned with 1 week grace 4-14