As you come in…

Sign in (in back) and pick up Badge Name Card – on computer…

Log in: Launch/Start Alice

Any questions? (of any kind) DOWNLOADS FOR TODAY:

http://ce21sandiego.org/2013 CylinderStarter.a2w Online student textbook (at bottom of each page

below) Module 9.2 Magnet World with Other Objects.a2w Module 9.4 SpaceShipGame.a2w

Today’s plan

While loops (penguin race, timer) Create your own function with a

parameter (timer) Compound boolean expressions and

if statements – can solve same problem multiple ways Or – car magnet And – space ship take off

Hint to getting while loops right

Humans naturally think “until” I’ll keep spending until I run out of money

(balance <= 0) I’ll keep dancing until I fall asleep

Computers use “while” loops – the opposite I’ll keep spending while I still have money

(balance > 0) I’ll keep dancing while I am not asleep While I have a dirty dish, I’ll keep washing

dishes

Let’s have a race…

A Wind up penguin (he just goes)

While loop with “walk and spin” inside it Jet-pack penguin2 (controlled by <- event)

Moves forward .5 meters Race to a stop sign (within 2 meters) Whenever someone gets within 2 meters

Stop looping (going)

While loops in Alice tend to be used when…

You have a user controlled (hence, not predictable) event So you don’t know when the user might

Click on an object Type a key, User types a number (pick a number between

1-10, etc. You have (not predictable) actions

controlled by, for example, random numbers E.g. the lunchlady/zombie or fish/shark case

When should we keep going?e.g. while loop expression true(P1: wind up, P2: jet pack)

Cases A B C DP1, P2 outside T T T TP1 inside, P2 outside T T T FP2 inside, P1 outside T T F FP1, P2 inside T F F F

Which while loop header (tile) would you use to control the “going”?

Let’s Build the Code!

Download from http://ce21sandiego.org/2013 Meeting 4: JetPackPenguinTeacherStart.a2w

Plan: Explore object positions Create event that moves jet pack penguin 0.5

meters whenever <space> is pushed. (Test) SIMPLIFY: Create loop that makes windup penguin

move repeatedly (forever), 0.35 meters (at same time as “walks” and windupKey “rolls” 0.25 revolutions)

CORRECT: change loop to have the game end (e.g. windup penguin stops walking) when either penguin “wins” (gets within 2 meters of stop sign)WHILE:_________________________________________

Game keeps playing while…A. Either penguin is close to the stop signB. Neither penguin is close to the stop sign

What does the other one do?

Useful tool: “Timer”

Use: to “count down time” in a game 2 “cylinder” objects set on top of each

other Grey is “background” Yellow is in “front”

Yellow moves down a bit each “time step” (loop iteration)

The game is over when the yellow cylinder is Distance to the ground >= cylinder height. (So while not, game is ongoing…)

Timer Coding Plan

SIMPLIFY: Loop forever (while true) move yellow cylinder down.

COMPLETE: Loop should stop after yellow cylinder

“disappears” – say should take 4 steps Hint: cylinder is 2 meters tall

After loop: have “3-D Text” (originally set to opacity 0) become visible saying “Game Over”

IMPROVE: Regardless cylinder size, calculate how many “steps” before cylinder gone 10 steps? 4 steps?

NEW PROGRAMMING CONCEPT: Functions – perform (complex) calculations

Compound Boolean Expressions – ORCar Driving Game (watch video 9.2)

Modify: Car should only turn to head towards MAGNETS One of the 4 magnets

Two ways if…

Compound Boolean Expressions – ORCar Driving Game

Two ways if…

Compound Boolean Expressions – ORCar Driving Game

Two ways if…

Compound Boolean Expressions – ANDSpaceship takes off

Space ship only takes off if all spheres are blue

Two ways if…

Compound Boolean Expressions – ANDSpaceship takes off

Two ways if…

Compound Boolean Expressions – ANDSpaceship takes off

Two ways if…

Functions: Calculate a Value and “Return” it.

Hides away complex calculation When program executes that line/tile:

change of control flow! Jump to code/function that does the

calculation It “returns” the calculated value, which

replaces the function call tile Finally, that line/tile is executed

Examples you know

Return number values: Move forward distanceTo Random

Create our own – which return boolean values isAMagnet areBallsBlue

Coming Up…

Week 5: Compound Boolean Expressions and if statements and while loops

Week 6: Functions, Mathematical expressions, parameters, methods

Week 7: Functions, parameters, methods and events

Week 8: Lists