Problem that I see regularly in the first years I TA - they're too overwhelmed by syntax and don't manage to break the problem down into bits so that they can code it.

1. Thinking Like a
Programmer
Cate Huston

2. What Does This Mean?
• For beginners, writing a (small) program should have
two main components.
• Understanding the problem and breaking it down
into small steps. Write these down on paper.
• Converting those steps into code with the
correct syntax. These steps should be max 2-3
lines of code for each step.
• These can be distinct - this can be helpful when
you’re learning.

3. Syntax
• Don’t worry so much about it!
• It’s easy to look up later when you convert your
logic to code.
• Google!
• Notes.
• Syntax varies between languages, but the
process of breaking the problem down is still
the same.

4. Photo by Flikr User anikarenina
Think of code constructs as building blocks that you
can use to assemble your program. It’s like lego, you
have to assemble something bit by bit.

5. Example 1: Persistence
• The persistence of a number is how many times you
have to replace the number by the sum or product of its
digits until one reaches a single digit.
• See: http://en.wikipedia.org/wiki/
Persistence_of_a_number
• Try and break this down into pieces. In this case, we will
calculate the product.
• Clue: we need two loops, one inside the other.
• These are called nested loops.

6. Example 1: Persistence
• Get in the initial number N
• P = 0 // Persistence is zero
• While N > 9
• tmp = 1 // 1 is neutral for multiplication
• for each digit D in N
• tmp = tmp * D
• P++ // add one to P
• N = tmp // update N with the new number
• Output P

7. Converting to Code
• Each of these lines of “pseudocode” require
at most 2-3 lines of code in any language.
• In many languages, they would require one
line line of code.
• If you don’t know how to convert anything,
look it up on Google or in your notes.

8. Example 2: Guessing
Game
• Let’s make a guessing game. We’ll break it down
into phases.
• Phase 1: The computer makes a random number,
and asks the user to guess it. It then confirms
whether or not the user got the number right.
• Phase 2: We give the user a limited number of
guesses.
• Phase 3: We allow the user to play again (if they
want).

9. Example 2: Guessing
Game: Phase 1
• Phase 1: Make a random number and ask
the user to guess it, confirm if they got it
right or not.
• Maybe you don’t know how to make a
random number, but just imagine you do -
it’s easy to look up if you decide to code
this.
• Try it!

10. Example 2: Guessing
Game: Phase 1
• R = random number 1-50
• N = guess from user
• if (R == N)
• Output “Well done!”
• else
• Output “You’re wrong!”

11. Example 2: Guessing
Game: Phase 2
• Phase 2: Give the user a limited number of
guesses
• We’ll need a boolean variable to keep track
if they’ve found it or not
• We’ll need a “for” loop to keep track of how
many guesses they’ve made and stop when
they’ve used them all up.
• Try it!

12. Example 2: Guessing
Game: Phase 2
• R = random number 1-50
• correct = false // they haven’t guessed it yet
• for i = 1 to 10
• // i is our counter, the user has 10 guesses
• N = guess from user
• if (R == N)
• correct = true
• exit loop
• next i
• if (correct)
• Output “Well done!”
• else
• Output “Wrong”

13. Example 2: Guessing
Game: Phase 3
• Phase 3: Allow the user to play again, if they
want.
• Use a while loop for this.
• Our code from Phase 2 will stay the same,
inside this loop.
• Try it!

14. Example 2: Guessing
Game: Phase 3
• continue = true // we’ll update this later
• do
• // code from Phase 2 goes here
• Output “Play Again? Y/N”
• response = input from user
• if (response == “N”)
• continue = false
• while (continue)

15. Photo by Flikr User fd
Try more examples, as many as you can find. Practice
breaking down the problem down into “code-able” pieces.
Don’t worry about syntax whilst you’re doing this.

16. @kittenthebad
http://www.catehuston.com/
catehuston@googlewave.com