CS 40 - Lecture 2

Cay S. Horstmann

Alice

• Learn basic lingo
• Carry out a simple task
• Gain confidence

Dealing with Complexity

• Computers are complex
  • more complex than algebra
  • less complex than a single-celled organism
• Need to dive in before you understand everything
• Not everyone's favorite learning style
• Set yourself simple task
• Be happy when you succeed

Rules of Engagement

• Work with your buddy
• Pair programming
• Submit your answers in eCampus
• Even if it is no good—no penalty
• Use ActiveLecture.org to give feedback
• Too boring? See penultimate slide

Anonymous Poll (No Wrong Answer)

Log in to http://ActiveLecture.org

How Do You Rate Your Computer Skills? (Email, word processing, etc.)

1. Excellent (know file system, keyboard shortcuts)
2. Good (get everything done without getting frustrated)
3. Fair (get stuff done but struggle a lot)
4. Poor (ofte challenged by simple tasks, can't complete tasks)
5. Other (please explain)

Your Mission

• Make an object hop around a circle

Learning Step 1: Invoke Methods

• Pick an object and add it to the world
• ...but not the same as your neighbors
• Make it hop once: Right click, select commands to
  • move up,
  • move sideways,
  • move down

What's the Point?

• Learn the system: Where to find stuff, where to click
• Learn the lingo: Objects, methods
• Are we done yet?
• No—doesn't hop around a circle
• Missing: Turns, repetitions
• Missing: Replay

Programming

• Programming = Making replay possible
• Programmer = Movie director
• Program user = Movie watcher
• Most programs can react to user input

Learning Step 2: world.my first method

• Program = sequence of canned steps
• Put step into world.my first method
• Usually start with a Do in order; drag it
• Drag in three toaster moves (but don't use a toaster)
• Click Play, watch it hop
• Repeat.
• You are a programmer!

Learning Step 3: Responsibilities

• Object-oriented programming: match objects and their responsibilities
• Should the world make the toaster hop?
• Should the toaster hop itself?
• Create new "hop" method for toaster (use your object)
• Drag code from world.my first method to toaster.hop
• What do you put into world.my first method? ← ActiveLecture.org

Learning Step 4: Loops

• Remember original goal: hop around a circle
• Turn a bit after each hop (try 0.05 revolutions; custom number)
• Hop, turn, hop, turn
• Add these calls to hip to world.my first method
• How many more calls do we need to add to go around the circle? ← ActiveLecture.org

Loops

• Drag Loop into world.my first method
• Drag a hop and turn into the loop; ditch the other
• Play and enjoy
• Did you solve our task?
• What did you learn? ← ActiveLecture.org

Too Boring?

• Make hopping smoother
• Make your object say something
• Vary radius of circle (Hint: Create new variable)

Reminder

• Save your world (hop.a2w)
• Upload to eCampus
• When working with a buddy, put in the buddy names (first and last!) in the comment field.
• Tonight, put your photo into eCampus