An “enjoyable” introduction to Programming

Dr. Jeyakesavan VeerasamyThe University of Texas at Dallas, USA

Email: jeyv@utdallas.edu Alice 2.2 Software: www.alice.org

Examples: www.utdallas.edu/~jeyv/alice

What is programming?

• Developing applications & games • Software is not limited to PC – most complex systems run software– smart phones, game devices, even DVD players

Programming …• is NOT a boring or repetitive activity• does NOT require you to sit in dark room and

type in computer all day! • does NOT involve complex Math

• requires logical thinking – technical common sense

• write minimal code & combine with existing components to build new applications

• Solve customers’ problems & improves quality of life for every one.

Why learn programming?

• Software Engineers get great pay!• Less stressful compared to several other high

paying jobs• Automation continues…• Computer touches our lives more & more every

day…• More component based programming always

room for simple programs to do large tasks!

Learning to ride bicycle

• Difficulties for beginners:

• Difficulties for experienced folks:

Learning to ride bicycle

• Difficulties for beginners:– Learning to balance & go forward together

• Difficulties for experienced folks:– None.

Solution for beginners

• Training wheels• Helmet

• Makes learning enjoyable and safe!

• Similar difficulties are there while learning to program in a computer.

Learning to program:Difficulties for beginners

Learning to program:Difficulties for beginners

1. Syntax errors • struggle for hours to fix syntax errors• Loose confidence • Frustrating experience• Run away & never come back if possible!

2. Logic errors Not a serious issue.

Difficulties for experienced programmers

Logic errorsContinuous learning

Learning to program

• Most students try to learn syntax and logic together, waste lot of hours and get confused & frustrated.

• Indian students resort to memorization of programs. US students run away from programming. Both are NOT good

• It is possible to do much better!

Solution

• Visual Programming Tools to teach programming concepts without encountering syntax errors.

• Focus on the logic first & build confidence.

Free Visual Programming ToolsTool Provider Web-site

Alice 2.2 Carnegie Mellon University, USA

www.alice.org

Scratch MIT, USA scratch.mit.eduSnap! UCBerkeley, USA byob.berkeley.edu

Lego MindStorm Lego, USA mindstorms.lego.com

Several more…

Sample program in Snap 4.0

Program Output

Programming Concepts

A few examples

• Recipe to make your favorite food• Assembly instructions for a toy• Coming to college from homeWhat is common about these activities?

A few examples

• Recipe to make your favorite food• Assembly instructions for a toy• Coming to college from homeWhat is common about these activities?

Sequence

Programming concepts:Sequence structure

instruction 1;instruction 2;instruction 3;…

A few more examples

• Study at home or play cricket with friends?• Eat Parotta or Poori?• Go to Vijay’s movie or Karthik’s movie?• Go to job or go for higher studies?What is the common thing here?

A few more examples

• Study at home or play cricket with friends?• Eat Parotta or Poori?• Go to Vijay’s movie or Karthik’s movie?• Go to job or go for higher studies?What is the common thing here?

Selection

Selection structure

IF condition is true THEN do this;ELSE do that;ENDIF

A few more examples

• Eat chips from a packet• Go on a shopping spree with lot of cash!• Take an exam that has several questionsWhat is the common thing here?

A few more examples

• Eat chips from a packet• Go on a shopping spree with lot of cash!• Take an exam that has several questionsWhat is the common thing here?

Repetition

Repetition structure

WHILE (more items to process) process the next item;ENDWHILE

FOR month = 1 to 12 do monthly processingENDFOR

Programming Concepts

• Structures: Sequence, Selection & Repetition• Foundation for Programming• Every complex program is only a combination

of these structures.

More things we do…

• Use a box to move lots of things from one room to another

• Carry a pack of candies to class on your birthday!

• What is the common thing here?

More things we do…

• Use a box to move lots of things from one room to another

• Carry a pack of candies to class on your birthday!

• What is the common thing here?

Collection / Arrays

Arrays

• enable us to store data of similar type together.

• enables us to handle varying size data.• Lines of code do not increase with more data!

FOR each item in array add item to total

ENDFOR

Even more things we do…

• Get phone call when you are driving a car• Friend knocks on the door when you are

watching a movie

• What is the common thing here?

Even more things we do…

• Get phone call when you are driving a car• Friend knocks on the door when you are

watching a movie

• What is the common thing here?

Interrupts / events

Event driven programming

• Suspend current processing to process the event, or process it in parallel.

• “Regular” processing flow & separate processing routine for each event.

Object Oriented Programming (OOP)

• Models the real-world better• Concepts learned from the manufactoring

industry

Hands-on Introduction to Alice

It is a good idea to save each program separately so that you can

go back and review later.

Purpose of Alice

• Enjoyable introduction to Programming• Natural introduction to OOP• Learning to program with training wheels• Stepping stone to learn more serious

languages (C/C++/Java)

Alice environment

• World• Gallery• Scene Setup– Adding objects– Working with objects

• Similar to Scene setup in move-making– Every object needs to be in starting position

Methods & Actions

• You are welcome to play along with me.• Add one object– Test out various movements (moves in 6

directions, turns in 4 ways & roll in 4 ways)• Add one more object– Test out relative movements

Program #1: Choose your favorite object from the gallery and test various methods.

10 minutes?

Our first program!

• Sequence structure• do a few interesting actions!

Program #2: Make your object do a few funny actions!

10 minutes?

Program #3

• Introduce multiple objects• do a few interesting actions!

Program #3: Make your objects do a few funny actions!

15 minutes?

Program #4

• Use DO TOGETHER structure• Add realism & sophistication!

Program #4: Use DO TOGETHER to do multiple things at same time!

15 minutes?

Program #5

• Add Vehicles/Seaplane from local gallery.• Make it do loop the loop.• Use DO TOGETHER structure– seaplane move forward– seaplane turn backward– seaplane’s propeller roll right

• Use “style = abruptly” to make the motion smooth

Program #5: Use DO TOGETHER to make the plane do loop the loop!

20 minutes?

Program #6

• Introduce repetition – counted loop• do a few interesting actions!

Program #6: Make your objects do a few funny actions multiple times!

10 minutes?

Program #7

• How to do realistic walking?• Leg & body movements• Better to do with a human object from

“People/Walking People”• Write your own methods.

Program #7: Practice human walking/running animation

15 minutes?

Program #8

• Walking back and forth between 2 points?• Use 2 objects as end-points.• What should you do when you get close to

those objects?

Program #8: Practice human walking/running back & forth.

15 minutes?

Program #9

• Alternate implementation of Program #8 using IF statement

• Can we use same code for step 1 and step 2?

Program #9: Practice human walking/running back & forth. Use variables and decision

structure

15 minutes?

Logical thinking

• You have been introduced to several building blocks – a few more on the way too.

• Now, it is all about putting/using them together in various combinations.

• I encourage you to think in high level, note down a few ideas (design), then proceed to implementation.

• Direct coding is NOT recommended.

Program #10: Lists/Arrays

Arrays cannot expand during run-time, but lists can. Alice supports more functionality with lists too. In simple words, lists are more powerful.

• Make a list of your favorite objects (multiple copies of an object is ok too!)

• Make them do something one at a time.• Make them do something in random order• Make them do something in sync.• You are not limited to these - use your imagination!

Program #10: Group & individual dance moves!Use similar objects so that you can work with

the parts too.

15 minutes?

Program #11: Events

• So far, we did everything under “my first method” or we invoked other methods from there.

• But when it comes to games or complex apps, user may press various buttons/items & we need to respond to each event.

Program #11: We will start with a coach and a ball. Coach keeps doing some exercise. We will use key based events to move the ball to top of his head. Then, coach should stop exercising and do something funny.

15 minutes?

Program #12: Frog’s jumping game!

• Swimming pool – moving lilypads – make the frog to jump on lilypads carefully and reach other side to win!

• Make the lilypads to move independently back and forth first. Then, work on the game.

• If the frog jumps and touches the water, it will sink! I guess this frog does not know to swim

• Plan and write the pseudocode first, before coding!

Program #12: Frog jumping game. Discuss/share ideas with your neighbour and help each

other to progress …

Move frog 0.7 meters forward when up-arrow is pressed.For moving lilypads, use distance (pool width – cricle width) with bit random speed.Use vehicle property to stick to lilypad.

High level idea/pseudocode #1move the frog by 0.7 meters.IF index is beyond lilypads

declare win!ELSE

IF frog is close to circles[index]frog is safe set vehicle for frog to corresponding circle

ELSEfrog dies! – make frog disappeardisplay a message

ENDIFENDIF increment index

High level idea/pseudocode #2move the frog by 0.7 meters.IF frog is close to “finish” object, declare win!ELSE

IF frog is close to any of the moving circlesfrog is safe set vehicle for frog to corresponding circle

ELSEfrog dies! – make frog disappeardisplay a message

ENDIFENDIF

Transition to C/C++/Java

• Most of you have become “mature” Alice programmers – you can see the limitations of Alice now.

• Now that your fundamentals are bit strengthened, this is a great time to get started with C/C++/Java!

• I encourage you to do the following problems in both languages: Alice and C/C++/Java.

• Time management is crucial – I encourage you to spend a few hours to solve programming problems periodically to strengthen your skills.

Transition to C/C++/Java: Math Practice program

• Display 2 random numbers (limit the range for each number to 1-100) and ask the user to multiply manually & input the result. Verify whether the user input is correct. Repeat it for 10 times, keep track of the score and display it in the end like this:

Your score: 8 correct, 2 incorrect.

Transition to C/C++/Java: Guessing Game

• First, guess a number between 1 and 100. Then, your program should ask you a series of questions and determine your guess based on your answers.

Question format: How about NN (<,=,>)? • Write the high level pseudocode, manually

verify it before proceeding to code.

Pseudocodeinitialize low = 1, high = 100WHILE low < high

mid = (low + high) / 2ask the user how about mid?IF user response is <

high = mid-1ELSE IF user resposne is >

low = mid+1ELSE IF user response is =

print great!break;

IF low == great print “Your guess is” low

ENDIF

Sample run #1 (user input in RED)

Guess a number between 1 and 100 (both inclusive)and get ready to answer a few questions.How about 50 (<,=,>)? <How about 25 (<,=,>)? <How about 12 (<,=,>)? >How about 18 (<,=,>)? >How about 21 (<,=,>)? <How about 19 (<,=,>)? >Your guess is 20.

Sample run #2 (user input in RED)

Guess a number between 1 and 100 (both inclusive) and get ready to answer a few questions.How about 50 (<,=,>)? >How about 75 (<,=,>)? <How about 62 (<,=,>)? >How about 68 (<,=,>)? =Your guess is 68.

Transition to C/C++/Java: Guessing Game

• Play the reverse game. Computer should guess a number between 1 and 100. Now, you should ask questions & determine that number.

• C/C++: use srand() and rand() to generate random numbers

• Write the pseudocode, manually verify it before proceeding to code.

Pseudocodeguess = Generate a random number 1 … 100Ask for user inputWHILE user input != guess

IF guess < user input output “<“

ELSEoutput “>”

Ask for user inputOutput “You guessed it right. Good game!”

Sample run

I have guessed a number. You can ask questions now.50<25<12>

18>21<19>20=Good job!

References

• Alice website: www.alice.org (download Alice 2.2 software)

• Textbook: Learning to Program with Alice by Wanda Dann, Steve Cooper and Randy PauschISBN: 0-1318-7289-3

• Free Ebook: www.dickbaldwin.com/tocalice.htm • My Alice examples: www.utdallas.edu/~

jeyv/alice