Instructions PLEASE READ (notice bold and underlined phrases)

Transcription

1 Assignment 2 Writing Basic Java Programs Required Reading Java Foundations Chapter 2 Data and Expressions Chapter 3 Sections , Chapter 4 Sections , Instructions PLEASE READ (notice bold and underlined phrases) This assignment has three parts: A. Written Answer the questions, submit a Word or PDF document B. Programming Code must be well commented, compile/test, then submit C. Submission Submit specified assignment files by deadline 1. This is an individual assignment. You may NOT work in teams for this assignment. You may discuss ideas with others, but you must answer all questions and write all the code yourself. You have reviewed the SFU Plagiarism guidelines. Please abide by them. Do not even copy a variable name that is plagiarism. Plagiarism hurts your learning process. Learn from others but do the work yourself and you will learn the material faster. Plagiarism by students will result penalties that may include receiving zero for the assignment. 2. All Files Submitted for Programming Assignments must include block comments for the Class and each Method. Block comments for the Class must include the name of the Java Class plus a short description of what the Class does. Comments should also include the Student s name and Student Number. Each Method should describe what the Method does, its parameters, and return values using JavaDoc compatible comments. 3. Submission deadline: 11:59pm Sunday Oct 6th. You should be able to complete the work if you have completed the required reading for the assignment. More material is available in the Class Slides. While you have seen most of what is discussed here, some topics discussed in this assignment and needed for your submission may not be seen until another class! You may submit before the deadline, if you so prefer. You may resubmit again later without penalty provided you resubmit before the deadline. 4. Keep a copy of everything you submit in your files. 5. READ. What is TRACE printing? Trace printing is a term to refer to additional printing that the programmer chooses to add while developing and debugging the program. With such printed information we are 1

2 tracing the execution of the program, that is, we, as programmers, are double checking what the execution of the program is and what some intermediate results are. The idea is that once the program is debugged (free of logical errors), those extra printing statements are commented out, as they are not meant to be seen by the user. For the exercises below, you are encouraged to add Trace Printing to your program to TRACE the program flow of control through the statements. Add the word TRACE in front of the trace printing to identify the extra printing so it will be easy to spot and remove. In some IDE s there are special tracing options that automate this process for you. Tracing is a very common (and needed!) practice among programmers in real life! It is an important skill to learn. In a future lab demo, we will learn better methods of watching program flow and for finding logic errors within your program as it runs. For now, you are encouraged to use println to find and correct errors in your program. This process is known as Debugging. The term comes from the days of ENIAC and its descendants that used relays and vacuum tubes to make up its computing circuits. These early computers were known to break down when insects would rest inside the relays. The debugging process was originally coined in those early days when they had to physically pick out the insects, the bugs, from the relays to get the computer working again. Today, the term Debugging is still used to mean finding computer program errors, the bugs, and fixing them. 6. READ. Another common and useful practice to debug programs (used in real life too!) is to run the code by hand (other terms may be used to refer to this activity also). The idea of hand tracing is to follow or simulate manually (using paper and pencil) what the different variable values are as the code is executing. This is particularly useful for small pieces of code and edge cases such as the first and last time through a loop. We will see examples of this during the course. 2

3 A. Written Assignment Answers to be submitted into CourSys Students may discuss the problems with fellow students, but students MUST complete the work on their own and the submitted answers must be your own work. Section A does not require any programming. Write your answers neatly in a document that will be submitted to CourSys as part of the assignment. Your document must be called a2writeup.doc or a2writeup.pdf and must include your name, student number, Course Name, Assignment Number, and Date along with your answers to the following questions. Use Courier font and double-space in your write up. 1. Operator Precedence 10 Marks Determine the operator precedence for the following expressions and evaluate each expression based on this precedence. Assume that the variables are defined as follows: int a = 1; int b = 2, int c = 3, int d = 4; int e = 5; double f = 10; In your submission, list each expression with your computed result, then write the order of evaluation under each operator. For example: (x) a + b + c + d Expected submission: (x) a + b + c + d = Determine operator precedence and evaluate the following: (a) a b c d (b) a b + c d (c) a + b / c / d (d) a + b / c * d (e) a / b * c * d (f) a % b / c * d (g) a % b % c % d (h) a (b c) - d (i) (a (b c)) d (j) a ((b c) d) 3

4 (k) a % (b %c) * d * e (l) a + (b c) * d e (m) (a + b) * c + d * e (n) (a + b) * (c /d) % e (o) (a + b + c + d + e)/ f (p) a + b + c + d + e + f (q) (a < b)!(c == d) (r) (a == b)? c : d (s) --a++ + a (t) a a + a 2. Generating Random Numbers 5 Marks Assuming that a Random object called generator has been created, what is the range of the result of each of the following expressions? (a) generator.nextint(20) (b) generator.nextint(8) + 1 (c) generator.nextint(45) + 10 (d) generator.nextint(100) Definite Loops 5 Marks Write a for loop to print the odd numbers from 1 to 99 (inclusive). You do not need to write a running program, just the for-loop and for-loop body. 4. Indefinite Loops 5 Marks Transform the following while loop into an equivalent do loop int num = 1; while (num < 20) { num++; system.out.println(num); } 4

5 B. Programming To be completed by Students Individually 1. Random Numbers 10 Marks Write a program with Class name RandomAvg that asks the user to specify the number of random numbers to generate. Your program should generate this number of random numbers from 1 to 100, print out each number, and then print the maximum number generated, the average with up to 3 decimal places, and the minimum number generated. Example test run: (user input is in BOLD) Enter how many random numbers you want to average: 3 Your 3 lucky random numbers are: Largest = 99 Average = Smallest= 2 2. Computing a Running Total and Average 10 Marks Write an application that reads a single line of input from the user containing at least one and up to 10 integers. Your program must compute the average. Pay attention to any conversions required. Print the average with to up to 3 decimal places. If any of the values entered by the user on the input line are non-integers or the user supplies too few or too many values, your program must discard the entire set of input and prompt the user to enter a new set of integers between 1 and 10. Your Java Class file should be called AvgNums.java. Example test run: Enter up to 10 numbers to average: 3 4 Average = Using the Math Class 10 Marks Write a program with Class name Distance that asks the user to enter the (x,y) coordinates for two points where both x and y must be integers. Compute the distance between the two points using the formula: distance = If any of the four coordinates are non-integers, your input validation should reject them all and ask for all four coordinates again. Your program must print the result with up to three decimal places. For 5

6 example, here is a sample run with the coordinates (0,0) and (8,2): Example test run: Specify two (x,y) coordinates as x1 y1 x2 y2: Distance from point(0,0) to point(8,2) = Making Change 15 Marks Write a program with a class called MoneyChanger whose main method prompts for and reads a double value representing a monetary amount. Then determine the least number of each Canadian bill and coin needed to represent that amount, starting with the highest (assume that a twentydollar bill is the maximum needed). If the entered value is not a double then your program must report an error and re-prompt the user for a double value. If, for example, the value entered is (fifty-seven dollars and sixty-three cents), then the program should print the equivalent amount as: Example test run: Enter monetary amount: $57.63 "$57.63" is not a double. Please enter a monetary amount as a double: That's equivalent to: 2 twenty dollar bills 1 ten dollar bill 1 five dollar bill 1 toony 0 loonies 2 quarters 1 dime 0 nickels 3 pennies 5. Counting Change and Program Decomposition 30 Marks Write another program with class name MoneyCounter that reads input from a user describing how many bills or coins of each type that they have using the same syntax as the output from Question 4 above. The program must keep a running total of the amount of money and print the final amount. Your program must skip over any input lines that do not start with an integer value or which do not have one of the following currency denominations as the second word on the same input line: 6

7 twenty ten five toonies toony loonies loony quarters quarter dimes dime nickels nickel pennies penny Your program should skip over any additional text on an input line after the number and the currency name. Your program should stop when there is no more input or when the user specifies the number of pennies. The word pennies or penny acts as a sentinel to tell your program to exit the input loop and print the total. Once out of the loop, the program should report how much total money was entered with the number formatted as a currency. Example test run: Enter the number of bills and coins you want counted. Please enter the number followed by the bill or coin name: 1 ten dollar bill But wait, I have more ten dollar bills coming! 5 ten dollar bills 1 quarter 1 ten dollar bills 3 pennies Your total amount of cash is: $70.28 Hint: Having programs read input characters with a specific syntax is called Parsing. Your program will need to use string comparison and if statements to check if a string token returned from the scanner matches any of the denomination strings above. You should use String.toLowerCase so your program is not case sensitive. You should handle the case where the coin or bill type is specified as singular or plural. For example: your code should be able to handle both dime and dimes and interpret both to represent units of ten cents. Parsing can get complicated and your main program should not have to worry about these details. Breaking a complex problem into two or more simpler problems is called Decomposition. This is how we go about solving complex problems. We break up a complex problem into several smaller ones that we can solve more easily. You will use decomposition a lot in this course and in the future. We will use decomposition here as well. This is the heart of Mañana Programming. Focus on the big details now, and worry about all the little details Mañana tomorrow. That is one secret to good design. Define an enum called CurrencyAmt to represent the above currency denominations as an enum data type. Include within the enum a special sentinel value called invalidcurrency. 7

8 Decompose your program by creating a static method within your class called parsecurrency that will accept a String parameter and return the corresponding CurrencyAmt value associated with that String, or return invalidcurrency if there is no matching currency denomination for that string. This will hide the complexity of parsing string currencies from your main program. Even before you fill in the implementation details of parsecurrency, you can continue working on your main program and make method calls to parsecurrency within main where appropriate. Do not worry that parsecurrency is not yet fully implemented, it will be Mañana. Complete the MoneyCounter program and test it by using the output of MoneyChanger as input into this program using cut/paste to copy the output from MoneyCounter into the input to MoneyChanger. The amount that you input into MoneyCounter should equal the amount printed by MoneyChanger when you use the output of first as the input to the later. 8

9 C. Submission To be Completed by Students Individually Student are responsible for submitting the requested work files by the stated deadline for full marks. It is the student s responsibility to submit on time. Submissions via will NOT be accepted. 1. You must submit your final version of the following files before the deadline. All written answers for Part A must be included in a single Word or PDF document which is double spaced and includes the Student s Name and Student Number at the top, along with the Course Number and Assignment Number. Students must ensure that all submitted code compiles and is properly commented and formatted for readability. Part A : a2writeup.doc or a2writeup.pdf Question B1 : RandomAvg.java Question B2 : AvgNums.java Question B3 : Distance.java Question B4 : MoneyChanger.java Question B5 : MoneyCounter.java 2. Files are to be submitted into CourSys under A02 as individuals. No group name is required and none should one be used. See the course website for submission instructions at: 9