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Homework 4

Homework 4. Sun., 9/29. ( MT sections ). Due. at midnight. Mon., 9/30. ( WTh sections ). Problems. http://www.cs.hmc.edu/courses/2002/fall/cs5/week_04/homework.html. CS 5 website. http://www.cs.hmc.edu/courses/2002/fall/cs5/. Submission problems?.

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Homework 4

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  1. Homework 4 Sun., 9/29 ( MT sections ) • Due at midnight Mon., 9/30 ( WTh sections ) • Problems http://www.cs.hmc.edu/courses/2002/fall/cs5/week_04/homework.html • CS 5 website http://www.cs.hmc.edu/courses/2002/fall/cs5/ • Submission problems? Don’t worry! email dodds@cs.hmc.edu or bthom@cs.hmc.edu and, if possible, include in that email your java files

  2. Tutors available academic computing labs (Parsons) Friday Afternoons 1-4 pm ------------------------------------------- Chris Hwang this week (9/20): Parsons Don Lee this week (9/20): Parsons Daniel Chan this week (9/20): LAC Lab Zach Andree this week (9/20): LAC Lab Annie Chang this week (9/20): LAC Lab Saturday Afternoons 1-4pm ------------------------------------------- Chris Weisiger this week (9/21): Parsons Yu-Min Kim this week (9/21): Parsons Elizabeth Lee-Su this week (9/21): LAC Lab Aaron Homer this week (9/21): LAC Lab Sunday Afternoons 1-4pm ------------------------------------------- Gabriel Neer this week (9/22): Parsons Jeff Brenion this week (9/22): LAC Lab Rene Logan this week (9/22): LAC Lab Linde Activities Center lab

  3. Tutors available Sunday evenings 7-12pm -------------------------------------------------- Jenny Xu 6-9 this week (9/22): Parsons Eric Flynn 7-10 this week (9/22): Parsons Melissa Federowicz 7-10 this week (9/22): LAC Lab Max Yi 7-10 this week (9/22): LAC Lab Yu-Min Kim 9-12 this week (9/22): Parsons A. Klose 9-12 this week (9/22): Parsons Matt Beaumont-Gay 9-12 this week (9/22): LAC Lab Chris Hwang 9-12 this week (9/22): LAC Lab Monday Evenings 7-12pm --------------------------------------------------- Adam Kangas 7-10 this week (9/23): Parsons Ryka Neher 7-10 this week (9/23): Parsons Max Yi 7-10 this week (9/23): LAC Lab Annie Chang 9-12 this week (9/23): Parsons Paul Scott 9-12 this week (9/23): Parsons John McCollough 9-12 this week (9/23): Parsons Alex Pipkin 9-12 this week (9/23): LAC Lab Chris Wottawa 9-12 this week (9/23): LAC Lab Alex Utter 9-12 this week (9/23): LAC Lab

  4. power base Problem 2: Power Generator • Power Generator Problem: Input a base and a power, find IMPORTANT! Do NOT use Math.pow( … ) Abstraction: taking a power is repeated multiplication for loop

  5. Problem 2: Power Generator CS5 Mantra: create structure first, then details double base; int power; //set above values via user double result; for ( ; ; ) //iteratively calculate power { } //display result

  6. for loops : Potential bugs //some higher-level vars int start = … , stop = … ; int someWork = … ; … 1 2 4 for ( int i = start ; i < stop ; ++i ) { //some lower-level vars int tmp; //do some calculation in here } 3

  7. Problem 1 - Sequence Generator Printing the first 9 terms of these sequences… 10 15 20 25 30 35 11 22 33 44 55 66 1 2 4 8 16 32 0 3 9 12 36 39 1 22 333 4444 55555 666666

  8. generating Random #’s CS5 Mantra: create structure first, then details Math.random(); produces a double between 0 and 1 (excluding 1) 0 1 3*Math.random(); produces a double between 0 and 3 (excluding 3) 0 1 2 3 (int)(3*Math.random()); produces an int between 0 and 2 (inclusive) 0 1 2 3 (int)(3*Math.random() + 1); produces an int between 1 and 3 (inclusive) 0 1 2 3

  9. potential Random # Bugs //following 2 don’t compile int r = (int)scale*Math.random() + offset; int r = offset + (int)scale*Math.random(); //only returns the value offset int r = offset + (int)Math.random()*scale; //a good one int r = offset + (int)(Math.random()*scale);

  10. Potential making-choices bugs if (choice == 1) { H.out.println(“good 1”); } if (choice == 2) { H.out.println(“good 2”); } if (choice == 3) { H.out.println(“good 3”); } else { H.out.println(“bad!”); } if (choice == 1) { H.out.println(“good 1”); } else if (choice == 2) { H.out.println(“good 2”); } else if (choice == 3) { H.out.println(“good 3”); { } else { H.out.println(“bad!”); } not necessarily mutually exclusive mutually exclusive blocks of code

  11. Problem 3 -- Monty Hall Welcome! I have an opportunity for you... Behind two of the following (virtual) curtains are cans of Spam, but behind the third is our grand prize! You may choose a curtain (1, 2, or 3): 1 All right, you've chosen curtain #1. Before showing you what you've won, however, I'm going to show you what's behind one of the curtains you did not choose... Behind curtain #3 was a can of Spam! A good thing you didn't choose that one, I guess. Now, you may stay with whatever is behind the curtain you initially chose, OR you may switch to the only remaining curtain -- which would you prefer, (switch or stay): switch You win! Behind curtain #2 was the car! Would you like to play again? yes

  12. Problem 3 -- Monty Hall Welcome! I have an opportunity for you... Behind two of the following (virtual) curtains are cans of Spam, but behind the third is our grand prize! You may choose a curtain (1, 2, or 3): 1 All right, you've chosen curtain #1. Before showing you what you've won, however, I'm going to show you what's behind one of the curtains you did not choose... Behind curtain #3 was a can of Spam! A good thing you didn't choose that one, I guess. Now, you may stay with whatever is behind the curtain you initially chose, OR you may switch to the only remaining curtain -- which would you prefer, (switch or stay): switch You win! Behind curtain #2 was the car! Would you like to play again? yes

  13. Problem 3 -- Monty Hall program skeleton randomly choose a winning curtain, 1-3 Welcome! I have an opportunity for you... Behind two of the following (virtual) curtains are cans of Spam, but behind the third is our grand prize! You may choose a curtain (1, 2, or 3): 1 All right, you've chosen curtain #1. Before showing you what you've won, however, I'm going to show you what's behind one of the curtains you did not choose... Behind curtain #3 was a can of Spam! A good thing you didn't choose that one, I guess. Now, you may stay with whatever is behind the curtain you initially chose, OR you may switch to the only remaining curtain -- which would you prefer, (switch or stay): switch You win! Behind curtain #2 was the car! Would you like to play again? yes input user’s initial choice need to find a losing curtain that was not the user’s choice ! get input compare to “switch” determine the user’s final choice & the result get input and continue or quit

  14. Problem 3 -- Monty Hall adding details randomly choose a winning curtain, 1-3 Welcome! I have an opportunity for you...

  15. Problem 3 -- Monty Hall adding details Behind two of the following (virtual) curtains are cans of Spam, but behind the third is our grand prize! You may choose a curtain (1, 2, or 3): 1 All right, you've chosen curtain #1. Before showing you what you've won, however, I'm going to show you what's behind one of the curtains you did not choose... Behind curtain #3 was a can of Spam! A good thing you didn't choose that one, I guess. input user’s initial choice need to find a losing curtain that was not the user’s choice !

  16. Problem 3 -- Monty Hall adding details Now, you may stay with whatever is behind the curtain you initially chose, OR you may switch to the only remaining curtain -- which would you prefer, (switch or stay): switch You win! Behind curtain #2 was the car! Would you like to play again? yes get input compare to “switch” determine the user’s final choice & the result

  17. Problem 3 -- Monty Hall adding details Would you like to play again? yes get input and continue or quit

  18. Android Monty! Variables Top-down software design • Curtain numbers (1,2, or 3) : car, spam1, spam2, user • When user switches curtain : change = true • car <--random--{1,2,3}; spam1, spam2 fully determined • query for user • Reveal spam1 or spam2 curtain (don’t reveal car!) • query for change • If • You win! • Else • You loose! Code Skeleton Until user quits

  19. Problem 4 • Monte Carlo Monty Hall Main idea: run your M.H. emulator 1000 times keep track of whether the user wins or loses Key details: no one is willing to play 1000 times! the program needs to play the part of the user, too • have the user always choose curtain #1 • have the user always switch • remove all printing except the final result of each trial print the number of wins and losses

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