1. This week in CS 5 HW 9 (2 problems) M/T sections W/Th sections due Sunday, 11/4 at midnight due Monday, 11/5 at midnight Recitation for HW9 -- Friday 11/2 A dizzying array of possibilities... Reading: Week 9’s online notes This week’s honorees are truly frightening... John Conway Carl Gauss

2. “Pass By Value” public static void main(String[] args) { int age = 18; H.out.print(“After a semester at HMC, you’ll feel ”); change(age); H.out.println(age + “ years old.”); } public static void change(int age) { age = 42; return; } PASS BY VALUE “Pass by value” means that data is copied when sent to a method

3. Passing Arrays by Value public static void main(String[] args) { int[] age = new int[2]; age[0] = 18; age[1] = 19; H.out.print(“After a semester at HMC, you’ll feel ”); change(age); H.out.println(age[0] + “ or ” + age[1] + “ years old.”); } public static void change(int[] age) { age[0] = 42; age[1] = 42; return; }

4. Watch out! public static void main(String[] args) { int[] age = new int[2]; age[0] = 18; age[1] = 19; H.out.print(“After a semester at HMC, you’ll feel ”); change(age); H.out.println(age[0] + “ years old.”); } public static void change(int[] age) { age = new int[2]; age[0] = 42; age[1] = 42; return; }

5. Arrays and Methods Engineers think their equations are an approximation to reality. Physicists think reality is an approximation to their equations. Mathematicians don't care. Simple Facts - > build structures from them Simple Actions (computations) -> build structures from them

6. 2d arrays Arrays can be of ANY type -- even other arrays! double[] arr; double[][] arr; arr = new double[nRows][nCols]; arr[0][2] = 10.0;

7. 2d arrays: Input and Output public static void main(String[] args) { double[][] arr = new int[3][4]; // getting the array from input for (int r=0 ; r<3 ; ++r) { for (int c=0 ; c<4 ; ++c) { bigarray[r][c] = H.in.nextDouble(); }

8. Using 2d arrays picture before & picture after -- fill in the code...

9. Problem 1 1 Display prices 2 Compute average of prices 3 Compute variance of prices 4 Display index and value of lowest price 5 Display index and value of highest price 6 Your TTS investment strategy 9 Quit Which choice would you like? Menu An array of different methods... Initial Input Get the number of stock prices from the user Then, get each stock price from the user into the array. Create an array of the appropriate number of elements.

10. Problem 1 How do we do this ? Pseudocode...

11. Methods What does this code do ? public static void main(String[] args) { } public static double sumArray(double[] arr) { double sum = 2.0; sum = sum + 40.0; return sum; }

12. Calling Methods What happens back in main() ?

13. Method notes double averageArray(double[] arr) double variance(double[] arr) int indexOfSmallest(double[] arr) int indexOfLargest(double[] arr)

14. Problem 2 0 1 2 34 5 0 1 2 34 5 0 1 2 34 5 A starting row of lights 2 is selected Each turn, a light is selected -- It and its neighbors switch states. Goal: get all the lights off… on off on

15. Problem 2

16. What is a light ? 0 1 2 34 5 How should we represent these lights in Java ? on off on

17. Lights Out -- Printing // draw the current set of lights 0 1 2 34 5 | |****|****|****| |****| | |****|****|****| |****| 0 1 2 3 4 5 6 7 lights should be separated with vertical bars may display all light numbers up to 15 print light numbers close to the center of each light “off” lights should be 4x4 blocks of spaces “on” lights should be 4x4 blocks of stars

18. H.out.println(“Type the number of words: ”); int len = H.in.nextInt(); String[] quip; quip = new String[len]; for (int i=0 ; i<len ; ++i) { quip[i] = H.in.nextWord(); } for (int i=len-1 ; i>=0 ; --i) { H.out.print( quip[i] + “ ” ); } Arrays in pictures int len String[] quip quip[0] quip[1] quip[2]quip[4] quip[3] 5 fall leaves after leaves fall i is 4 i is 3 i is 2 i is 1i is 0 fall leaves after leaves fall

19. public static int numSyllables(String w) { int numSyls = 0; int len = w.length(); if ( isVowel(w.charAt(0)) ) // an initial vowel ? ++numSyls; for (int i=1 ; i<w.length() ; ++i) { // vowel preceded by a consonant if ( isVowel(w.charAt(i))&& !isVowel(w.charAt(i-1)) ) ++numSyls; } // final ‘e’ preceded by a consonant if ( w.charAt(len-1) == 'e’ && len >= 2 && !isVowel(w.charAt(len-2)) ) --numSyls; if (numSyls < 1) // every word has at least 1 syllable numSyls = 1; return numSyls; } Syllable counting

20. Take in a number of words and print them out in reverse order. (To be specific, suppose it’s 5 words.) A puzzle...

21. Take in a number of words and print them out in reverse order. (To be specific, suppose it’s 5 words.) A puzzle... String s1 = H.in.nextWord(); String s2 = H.in.nextWord(); String s3 = H.in.nextWord(); String s4 = H.in.nextWord(); String s5 = H.in.nextWord(); H.out.print( s5 + “ ” ); H.out.print( s4 + “ ” ); H.out.print( s3 + “ ” ); H.out.print( s2 + “ ” ); H.out.print( s1 + “\n” ); Not a very flexible solution...

22. Arrays - lists of data items String[] quip; quip = new String[5]; for (int i=0 ; i<5 ; ++i) { quip[i] = H.in.nextWord(); } declares a String array named quip declares five String s named quip[0]…quip[4] loop through the array index

23. Arrays in code H.out.println(“Type the number of words: ”); int len = H.in.nextInt(); String[] quip; // create an empty array quip = new String[len]; // create array elements for (int i=0 ; i<len ; ++i) { quip[i] = H.in.nextWord(); // input each element } // now print them out in reverse order…

24. Sentence palindromes bores are people that say that people are bores fall leaves after leaves fall you can cage a swallow, can’t you, but you can’t swallow a cage, can you? First Ladies rule the state and state the rule, “Ladies First!”

25. Strings Be careful not to go out of bounds! Element types double, int, String, boolean, char, (any type) … char The ith element Example Declaration Length arr[i]s.charAt(i) double[] arr; arr = new double[100]; String s; java.lang.StringIndexOutOfBoundsException: -1 java.lang.ArrayIndexOutOfBoundsException: -1 arr.lengths.length() Warning Range from 0 up to length-1 vs Arrays

26. T. T. Securities Input stock prices for a number of days in a row, and then analyze that data…. 1 Display prices 2 Compute average of prices 3 Compute standard deviation of prices 4 Display index and value of lowest price 5 Display index and value of highest price 6 Your TTS investment strategy 9 Quit Which choice would you like? Menu:

27. Arrays and Methods public static double sumArray(double[] arr)

28. Using sumArray public static void main(String[] args) { // prompt for and input nStocks double[] stocks = new double[nStocks]; // input and assign each stocks[i] double stockSum = sumArray(stocks); H.out.println(“The sum is ” + stockSum); } public static double sumArray(double[] arr) { // see previous page … return sum; } double[] stocks 90.0 10.0 60.042.0 75.0 70.0 double[] arr

29. Using sumArray public static void main(String[] args) { // prompt for and input nStocks double[] stocks = new double[nStocks]; // input and assign each stocks[i] double stockSum = sumArray(stocks); H.out.println(“The sum is ” + stockSum); } public static double sumArray(double[] arr) { // see previous page … return sum; } double[] stocks 90.0 10.0 60.042.0 75.0 70.0 double[] arr 2 references referring to the same list of data

30. Array Searching public static double findMax(double[] arr)

31. T. T. Securities Find the most profitable strategy for buying and selling the stock among the prices in the array... Day 0 Price is 90.0 Day 1 Price is 10.0 Day 2 Price is 60.0 Day 3 Price is 42.0 Day 4 Price is 75.0 Day 5 Price is 70.0

32. Lights Out ! 0 1 2 34 5 0 1 2 34 5 0 1 2 34 5 A starting row of lights 2 is selected Each turn, a light is selected -- It and its neighbors switch states. Goal: get all the lights off… on off on

33. Lights Out ! Features of the game: // allow the user to set the // number of lights from 3 to 15 // start each light randomly on or off // draw the current set of lights // allow the user to select a light // only allow valid lights ! // update the set of lights and repeat

34. Lights Out ! // draw the current set of lights 0 1 2 34 5 | |****|****|****| |****| | |****|****|****| |****| 0 1 2 3 4 5 6 7 lights should be separated with vertical bars may display all light numbers up to 15 print light numbers close to the center of each light “off” lights should be 4x4 blocks of spaces “on” lights should be 4x4 blocks of stars

35. Lights Out ! // allow the user to select a light // only allow valid lights !