Pencil-and-Paper Exercises (15 points total)

Transcription

1 Computer Science E-50a: Introduction to Computer Science Using Java, I Handout part 1 I.Description Refer to the Savitch text (or your favorite Java reference) to reinforce your comprehension of Java parameter passing mechanisms and other constructs. Unless otherwise indicated, everything which the human would type to the computer has been underlined. Everything which the computer types is not. Work carefully! The programming problems which are done on the computer will be graded partly on the basis of style as well as correctness. These problems are due prior to the start of lecture on Monday evening, April 14. Get started as soon as possible! II. Pencil-and-Paper Exercises (15 points total) [1] 5 points Write Java code (it doesn t have to be a complete program) that generates two random integers, each between 1 and 7 (inclusive). Use a switch statement to output one of the following three messages: A tie! if the difference between the numbers is zero You lose! if the difference between the numbers is 1, 3, or 5 You win! if the difference between the numbers is 2, 4, or 6 Spring 2003 Dr. S. J. Eigen

2 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 2 [2] 5 points Precisely what is printed by the following horrible program? In answering this question, draw little boxes that clearly show how the values of all the different variables change as each instruction gets executed. (We want you to demonstrate that you understand how parameter passing works!) class Prob2 { static int foo (int a, int b) { return (a + b); } static int bar (int x) { x += 2; return (x * x); } } public static void main (String args[ ] ) { int x = 2; System.out.println("Foo = " + foo(x, 3) ); System.out.println("Foo = " + foo(x, 4) ); System.out.println("Bar = " + bar( -x )); System.out.println("Bar = " + bar( foo(x+x, ++x) )); } [3] 5 points In Java s Character class, there s a method named isjavaidentifierstart(char ch). This method determines if the char argument is permissible as the first character in a Java identifier. A character may start a Java identifier if and only if it is (1) a letter; (2) a currency symbol (i.e., $ ); or (3) a connecting punctuation character (i.e., _ which is the underscore). This method returns true if the character may start a Java identifier; false otherwise. Define your own version of isjavaidentifierstart

3 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 3 III. Programming Problems (up to 100 points) For the problems in this section, be sure to follow the instructions on electronic submission as described in [4] 15 points (use file ThisOldMan.java) Write a program to print the lyrics for the song This Old Man. This old man, he played 1. He played nick-nack on my drum; With a nick-nack paddy-whack, give the dog a bone, This old man came running home. This old man, he played 2. He played nick-nack on my shoe; With a nick-nack paddy-whack, give the dog a bone, This old man came running home. Use the same technique demonstrated in lecture for the Marching Ants song. The remaining verses are 3 on my tree 4 on my door 5 on my hive 6 on my sticks 7 up in heaven 8 on my gate 9 on my spine 10 on my hen Alternative lyrics, as well as other nursery rhymes appear at

4 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 4 [5] 10 points (use file LeapYear.java) Write a predicate method static boolean isleapyear(int year) that tests whether its argument repesents a leap year, i.e., a year with 366 days. Leap years are necessary to keep the calendar synchronized with the sun because the earth revolves around this star once every days. Actually, that figure is not entirely precise, and so for all dates after 1582 the Gregorian Correction applies: the years that are divisible by 4 are usually leap years (for example, 1996). However, years that are divisible by 100 (for example, 1900) are not leap years; but years that are divisible by 400 are leap years (e.g., the year 2000). Write a main method that tests your isleapyear method. It should work as shown here asking the user for a year until the value -1 is typed. The year value that is input should be passed to the isleapyear method, which then computes and returns the answer that gets printed by your main program. Type a year greater than 1582, or -1 to stop: IS a leap year! Type a year greater than 1582, or or -1 to stop: IS NOT a leap year! Type a year greater than 1582, or or -1 to stop: IS a leap year! Type a year greater than 1582, or or -1 to stop: -1 Thank you for using this program! For those of you interested in the background of leap years, Sarah L. Maher w/information provided by Royal Greenwich Observatory has written the following. See also Our solar year (the time required for Earth to travel once around the Sun) is days. Our calendar year is either 365 days in non leap years or 366 days in leap years. A leap year every 4 years gives us days, sending our seasons off course and eventually in

5 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 5 the wrong months. hundred years or so. To change.25 days to.24219, we skip a few leap days every one Here s the history: The Romans originally had a 355-day calendar. To keep up with the seasons, an extra 22 or 23-day month was inserted every second year. For reasons unknown, this extra month was only observed now and then. By Julius Caesar s time, the seasons no longer occurred at the same calendar periods as history had shown. To correct this, Caesar eliminated the extra month and added one or two extra days to the end of various months (his month included, which was Quintilis, later renamed Juliuswe know it as July). This extended the calendar to 365 days. Also intended was an extra calendar day every fourth year (following the 28th day of Februarius). However, after Caesar s death in 44 B.C., the calendars were written with an extra day every 3 years instead of every 4 until corrected in 8 A.D. So again, the calendar drifted away from the seasons. By 1582, Pope Gregory XIII recognized that Easter would eventually become closer and closer to Christmas. The calendar was reformed so that a leap day would occur in any year that is divisible by 4 but not divisible by 100 except when the year is divisible by 400. Thus 1600 and 2000, although century marks, have a Leap Day. The calendar we use today, known as the Gregorian calendar, makes our year days only off from our solar year by.00031, which amounts to only one day s error after 4,000 years. [6] 15 points (use file License.java) Write a Java program that prints 20 random license plate numbers, each one consisting of three randomly-chosen digits followed by three randomly chosen upper-case letters. The first digit cannot be zero.

6 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 6 [7] 15 points (use file Initials.java) Write a Java method named getinitials that accepts a String value in its only parameter. Assume the actual argument passed to this parameter is some person s full name and contains their first, middle and last names. This method should return a String containing this person s initials. Use the built-in String methods such as length(), charat(), compareto(), indexof(), concat(), and so on. For example, getinitials( William H. Gates, III ) should return the value WHG. Assume that precisely one space character separates the first name from the middle name, and the middle name from the last name. Be sure you write a main method that tests your program out thoroughly; it should read in a character string that the user types on the keyboard using one of the SavitchIn methods. Describe carefully whether and why your method will fail if you pass as an argument to it a String that lacks a middle name. [8] 15 points (use file Nim.java) Write a program that plays a complete game of Nim against a human opponent. In this very simple game, the players start with a pile of 11 match sticks. Each player takes a turn at removing one, two, or three matches from the pile. The player that ends up with the last stick is the loser. Here s a simple interaction to illustrate how your program will look in action: WELCOME TO THE GAME OF NIM! How many matches do you want? -1 That s an illegal move. Choose 1, 2, or 3 matches. How many matches do you want? 1 Human takes one match, leaving 10 Computer takes 1 match, leaving 9 How many matches do you want? 1

7 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 7 Human takes one match, leaving 8 Computer takes 3 matches, leaving 5 How many matches do you want? 2 Human takes 2 matches, leaving 3 Computer takes 2 matches, leaving 1 Computer wins the game! Note that the human always goes first, and whenever the human makes a stupid move, the computer will win the game. If the computer is in a situation where it knows it cannot win (e.g., it has 5 matches), have it pick an appropriate random number of matches. Note also that the output from the program is grammatical. By this we mean the program prints the singular and plural forms of the word match correctly (e.g., 1 match versus 2 matches ). Also note that the program will not allow the human to make an illegal move. Use a switch statement in the part of your program that deals with the computer s strategy.

8 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 8 [9] 10 points (use file Baseball.java) THIS PROBLEM IS REQUIRED FOR ALL GRADUATE-CREDIT STUDENTS. Undergraduate-credit students may solve the problem for extra credit. Johann VanDerDoe, a baseball player, has the following lifetime hitting percentages: Out 63.4% Walk10.3% Single 19.0% Double 4.9% Triple 1.1% Home run 1.3% Using random numbers write a Java program to simulate 1000 times at bat for Johann, counting (and printing out) the number of outs, walks, singles, and so on, and then calculating his batting average, which is (# of hits) / ( # of walks) Note that singles, doubles, triples and home runs are all considered to be hits. Hint: if the random numbers you generate are each between 0 and 1, then a random number which is less than or equal to.634 should count as an out. Random numbers greater than.634 but less than or equal to.737 represent a walk, and so on. Think about it! [10] 10 points Given the time of day in terms of an hour, minute, second and day half (i.e., AM or PM), write a static Java method named fractionofday to calculate and return the fraction of the day (a value of type double) that has elapsed since midnight (12:00 AM). For example, System.out.print(fractionOfDay ( 12, 0, 0, 'A')); would print 0.0 System.out.print(fractionOfDay ( 12, 0, 0, 'P')); would print 0.5 System.out.print(fractionOfDay ( 11, 59, 59, 'P')); would print Write a main method that can produce a table like the following (use a

9 Computer Science E-50a: Introduction to Computer Science Using Java, I Page 9 couple of for loops): Time Fraction since midnight 12:00 AM 0 1:00 AM :00 AM :00 AM :00 AM :00 AM :00 AM :00 AM :00 AM :00 AM :00 AM :00 AM :00 PM 0.5 1:00 PM :00 PM :00 PM :00 PM :00 PM :00 PM :00 PM :00 PM :00 PM :00 PM :00 PM