Thinking Like a Programmer

Thinking Like a Programmer

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  Thinking Like a Programmer Cate Huston
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  What Does ThisMean? • 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.
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  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.
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  Photo by FlikrUser 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.
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  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.
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  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
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  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.
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  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).
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  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!
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  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!”
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  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!
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  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”
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  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!
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  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)
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  Photo by FlikrUser 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.
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  @kittenthebad http://www.catehuston.com/ catehuston@googlewave.com