Algorithms and Conditionals

Transcription

1 August 26, 2013

2 Charactaristics of an Algorithm Charactaristics of an Algorithm Calculating Monitor Size if

3 Charactaristics of an Algorithm Calculating Monitor Size 5 charactaristics of a good algorithm: 1. Defined inputs 2. Defined outputs 3. Complete (no implied steps) 4. All steps are doable by a computer 5. Finite (finishes eventually) Number 5 above is an issues once we start using loops

4 Calculating Monitor Size Charactaristics of an Algorithm Calculating Monitor Size Input: Diagonal size (diagonal), ratio (a, b) diagonal 1. Store the result of 2 in X 1 a 2 +b 2 2. Calculate a X, store in side1 3. Calculate b X, store in side2 4. Calculate side1 side2, store in Size Output: Size, side1, side2 1 X is something I made up years ago. I ve since forgotten what it was supposed to represent, but it does make the calculation work.

5 if The if statement Do something based on a condition Many real-world equivalents (if you clean your room, then you can have cake for dinner) The condition must be something a computer can figure out! Example 1: if x > y... Example 2: if y 4 < x and y > z... General form for an algorithm if statement (not correct MATLAB): if condition then Thing(s) to do if condition is true end if

6 if Example: Guess the number! Input: Two guesses, guess1 and guess2, plus the secret number (secret) 1. if guess1 secret < guess2 secret then 2. store First guess was closer! in message 3. end if 4. if guess1 secret > guess2 secret then 5. store Second guess was closer! in message 6. end if 7. if guess1 secret == guess2 secret then 8. store Tie! in message 9. end if Output: Message indicating which guess was closer

7 if Similar to the English otherwise If you clean your room, you can have cake for dinner. Else, you can have a single uncooked potato for dinner. Allows you to avoid repeating conditions over and over. General form: if condition then Thing(s) to do if condition is true ( then is generally not used here) Thing(s) to do if condition is false end if Indentation is starting to matter - see next example

8 if Guess the number, improvement 1 Input: Two guesses, guess1 and guess2, plus the secret number (secret) 1. if guess1 secret < guess2 secret then 2. store First guess was closer! in message if guess1 secret > guess2 secret then 5. store Second guess was closer! in message store Tie! in message 8. end if (For the first if ) 9. end if (For the second if ) Output: Message indicating which guess was closer

9 if if ( if ) If you clean your room, you can have cake for dinner. Elsif you clean the litter box, you can have soup for dinner. Else, you can have a single uncooked potato for dinner. This is a more elegant way to write the last example if is the word MATLAB uses. Some other languages use elif, or simply if General form: if condition then Thing(s) to do if condition is true if second condition then Thing(s) to do if condition is false, and second condition is true ( then is generally not used here) Thing(s) to do if condition is false end if

10 if Guess the number, improvement 2 Input: Two guesses, guess1 and guess2, plus the secret number (secret) 1. if guess1 secret < guess2 secret then 2. store First guess was closer! in message 3. if guess1 secret > guess2 secret then 4. store Second guess was closer! in message store Tie! in message 7. end if Output: Message indicating which guess was closer

11 if quiz Write an algorithm to determine the maximum of three numbers Input: A, B, and C Output: Maximum of the three You don t need to figure out which one was biggest, just what the maximum of the three is. Watch out for ties! The maximum of 3, 5, and 5 is 5. If it helps, you can use or. Not due. Just see if you can do it for your own sake.

12 What an algorithm is How if statements work in an algorithm (including and if) (After doing the quiz) the ability to write simple algorithms.