1. Simple Control Structures

2. What will we learn today?
We will learn
Simple Control Structures
Conditional statement
How an if/else statement is processed
Example
Relational Operators

3. Control Structures
Control Structure: is a programming statement that allows you to control the order in which instructions are executed
Examples
Do together, do in-order
Conditional execution (if/else statement)
Repetition (loops)

4. Conditional Statement
It is a control statement depends on a decision
When a decision is being made a question is asked about certain condition in the world “e.g. is Ahmed taller than Ali?”
The answer is a Boolean value either True (yes) or False (no)
Some condition is checked and a decision is made about weather/not a certain section of program code is executed
Decisions are useful when some instructions are executed to run only under certain condition

5. If/else Statement
In Alice, if/else statement is used to control whether a block of instructions is executed or a method is called
An if statement contains a ‘Boolean Condition’ used to determine whether the part of code will execute
When the Boolean condition evaluates to
True, the If part of the statement will execute (run)
False, the else part will execute
The statement checks to see weather a condition is true, if condition is true one statement of program instruction is run. Otherwise a separate set of a program is run

6. How an If/else Statement is Processed
True False
It is possible that no action would be expected for one of the parts in the flowchart
True False
Do This
Action
Do Something
Else
Is condition
True
Do this
Action

7. Boy and Cat Example
The cat is sitting on a table and the little boy wants to catch it
If the boy is shorter than the table, he can jump to get the cat
Else, he can hold the cat easily
The question is how to know which is taller the little boy or the table?
Use function is shorter than of the boy object

8. Create an If/else Statement
How to create an if statement in Alice
Drag the if/else tile into the editor
Select the initial condition from the popup box
Drag the boy’s is shorter than function and put it in the place of true in the editor
If the answer is true, the if part is executed and else part skipped.
If the answer is false, if part is skipped and else executed

9. The Resulting Animation

10. Relational Operators
Alice provides 6 relational operators grouped together in the math category of world’s built-in functions
They work the same way as they do in mathematics
(== is equal to)
(!= is not equal)
(> is greater than)
(< is less than)
(>= is greater than or equal to)
(<= is less than or equal to)

11. Boy and Cat Example
Using a relational operator to write your own condition
Assume that the boy is 1 meter tall, write if statement that checks the boy’s height against 1 meter
If the boy’s height is less than 1 meter
Do in order
Boy moves up
Boy moves down
Else
Do nothing

12. Create your own Boolean Expression
Drag the if tile into the editor
Drag the world function (a<b) on top of the true tile in the if statement
From the popup menu select 1 for a and 2 for b as a placeholder
Drag the boy’s height function to replace 1
Inside if part, add a do in-order block and instructions to make the boy jumps up
Else, do nothing

13. The Resulting Statement

14. Let’s Work with Alice
The SpiderRobot (Scific) is moving in the space, it encounters a rock and it wants to see if there is something behind the rock or not. Write an animation to implement this storyboard
If the spiderRobot is shorter than rock
Do in Order
spiderRobot neck move up
spiderRobot neck move down
Else
Do nothing