Homework 3

• Due ( MT sections )

( WTh sections )

at midnightSun., 9/21

Mon., 9/22

• Problems

http://www.cs.hmc.edu/courses/2003/fall/cs5/

http://www.cs.hmc.edu/courses/2003/fall/cs5/week_03/homework.html

• CS 5 website

come see me or email me at dodds@cs.hmc.edu

• Submission problems? Grade Concerns?

• Tutors available -- contact information

• Tutors available -- lab places and times

You may also seek out tutors away from the labs, by phone, in the dorms, etc.

Available in the LAC Lab (Linde Activities Center)

Available in Parsons PC Labs (the CIS classrooms)

Problem 3: Rock-Paper-Scissors

overall structure first…

you might want to use the “Evens and Odds” code available at www.cs.hmc.edu/~dodds/cs5 as a starting point

Problem 3

• choosing rock, paper, or scissors...

class CS5App { public static void main(String[] args) { H.pl(“Welcome to RPS!”); H.p(“Be prepared for my”); H.pl(“AVALANCHE strategy!”);

String cc = “”; // cc is computer’s choice

How do we make the real choice?

Why is this value here?

Problem 3

• Let the user choose rock, paper, or scissors

H.pl(“What do you show -- ”);H.p(“rock, paper, or scissors? ”);

String uc = H.nl();Three things are going on here !?!

Problem 3

• Let the user choose rock, paper, or scissors

• Both players have chosen -- what happens next ?

H.pl(“What do you show -- ”);H.p(“rock, paper, or scissors? ”);

String uc = H.nl();

if ( )

{

}

Lots of Cases!

computer chose “rock”user chose “paper”

Three things are going on here !?!

Problem 2 -- Math Menu

• Menu of 6 options:

Please choose one of these options:

(0) A friendly (and random) message(1) Power computing!(2) Prof Saeta’s physics function (!*?%!)(3) Convert from seconds(4) Convert to seconds(5) Find the max and min of 4 different ints

Choose an option (0-5):

computer scientists tend to start counting from 0, instead of 1…

There are really seven cases to consider -- why?

Problem 2 -- getting started

• create the general structure of the program then fill in details

Outline of code:problem decomposition…

you might want to use the “Moth Menu” code available at www.cs.hmc.edu/~dodds/cs5 as a starting point

Different ways of making choices

if … if … if …

not necessarily mutually exclusive

if … else if … else if … else

mutually exclusive blocks of code

if … else

if (choice == 0){}if (choice == 1){}if (choice == 2){}else{}

if (choice == 0){}else if (choice == 1){}else if (choice == 2){}else{}

Different ways of making choices

switch

mutually exclusive blocks of code as long

as you use break !

switch (choice){ case 0: { break; }

case 1: { break; }

default: { }}

Why is there no need for a break in this last case?

Problem 2 -- option 0

• creating a random message… (create the structure first, then details)

Math.random();

recurring theme

produces a double between 0 and 1 (excluding 1)

but, you need to store this random number somewhere!

0 1

0 1 2 3

produces a double between 0 and 3 (excluding 3)

produces an int between 0 and 2 (inclusive)

0 1 2 3

produces an int between 1 and 3 (inclusive)

0 1 2 3

Problem 2 -- option 2

Period of a pendulum (almost!)

What variables will we need?

Problem 2 -- option 2

Period of a pendulum (almost!)

How to compose these operations and functions together?

Problem 2 -- option 3

• from seconds years, days, hours, minutes, and seconds

How many years are in 1,000,000,000 seconds?

31536000 sec/year

86400 sec/day

3600 sec/hour

60 sec/min

Problem 2 -- option 4

• from years, days, hours, minutes, and seconds seconds

How many seconds are in 42 years?

problem outline:

Problem 2 -- option 5

Finding the max and min of four different ints.

/* * Be sure to fill in this comment... */

import HMC.*;

class CS5App { public static void main(String[] args) { int a, b, c, d;

H.out.println(“Input four integers:”); a = H.in.nextInt(); b = H.in.nextInt(); c = H.in.nextInt(); d = H.in.nextInt();

Input

Problem 2 -- option 5

// is a the smallest among them ?

if ( ) { H.out.println(“The smallest integer is ” + a); } // is b the smallest among them ?

if ( ) { H.out.println(“The smallest integer is ” + b); } // and so on… // with a similar construction for the max

Min

Problem 2 -- option 5

How many comparisons will this take (in the worst case)?

Problem 1

• The Virtual Lyricist or, perhaps, conversationalist

class CS5App { public static void main(String[] args) { H.p(“Enter your favorite mascot: ”); String mascot = H.nl();

H.pl(“Here we go, ” + mascot); H.pl(“Here we go!”); }}

Use at least 4 variables

What’s the effect of this H.p?

Problem 1

class CS5App { public static void main(String[] args) { H.p(“Enter your favorite mascot: ”); String mascot = H.nl();

H.pl(“Here we go, ” + mascot); H.pl(“Here we go!”);

H.p(“Enter an enemy mascot: ”); String mascot = H.nl();

H.pl(“Here we go, ” + mascot); H.pl(“Here we go!”); }} What’s wrong here?!

Problem 1

class CS5App { public static void main(String[] args) { H.p(“Enter your favorite mascot: ”); String mascot = H.nl();

H.pl(“Here we go, ” + mascot); H.pl(“Here we go!”);

H.p(“Enter an enemy mascot: ”); mascot = H.nl();

H.pl(“Here we go, ” + mascot); H.pl(“Here we go!”); }}

declaring the variable -- can be done once!

assigning the variable -- can be done any time...

using the variable -- done any time...

Input: Know your type!

H.in.nextWord();H.in.nextLine();

H.in.nextInt();

H.in.nextLong();

H.in.nextChar();

H.in.nextDouble();

H.in.nextAnyChar();

H.nw();H.nl();

H.nc();H.nanyc();

H.ni();

H.nlong();

H.nd();shortcuts !

return a String

return a char

returns an int

returns a long

returns a double

including whitespace

including whitespace

Style

/* * Author: me! * Date: 9/20/03 * Homework 3 * Problem 2 * Comment: I spent 10 hours on this problem * (in binary) */

class CS5App { public static void main(String[] args) { H.p(“Enter your favorite mascot: ”);

String mascot = H.in.nextWord(); … more code here … }}

leave space before blocks of code

leave space between parts of code that do different things

introductory comment

indent code evenly within the surrounding braces

align curly braces that correspond

use reasonable variable names