ITEC120

hw02i, hw02g:
Practice writing functions; using Strings

Instructions for all programs

As with all programs for this class, you need to include:

• A short comment preceding each function, explaining what it takes in and what it returns. (Be sure to include the units--that is, GB and minutes, for this problem.)
• Test cases. Since you need to turn this in anyway, you might as well type them in comments preceding your function. The format you've used since 8th grade arithmetic is best:

  /* Test cases: * GB2min( … ) = … * … */

• Clear indentation, variable names, no spelling errors, and otherwise readable code.
• No magic numbers! (Use named constants, using final.)
• No repeated code!
• Do not use Java keywords which we haven't mentioned in class¹. (Part of understanding a problem well, is coming up with solutions which don't overly-complicate simple requirements.) This means you'll need to use an environment like BlueJ², rather than Eclipse or JCreator, for now. Furthermore, do not yet use System.out.println, even though we may start discussing this³ at the end of week 2 start of week 3.
• turn-in: Bring a hard-copy (printout) to class of your Java code. On WebCT, electronically attach your code file, whose name is the same as your class's name (first line of your file); it will either end in .java or have no suffix at all (but Windows Explorer will tag it as a Java file). The file will be located inside the BlueJ project folder. Do not bother turning in the other files (with suffixes like .class or .pkg).

hw02i, due Sep.01 (Fri) ⁴

1. (10pts, GB2min)

   Do this problem individually.

   You are shopping for mp3 players, and are wondering how much storage you need for your music files. You decide that 1GB of storage⁵ holds 940 minutes of music, approximately⁶. Write a function GB2min which converts a number of GB to an estimated number of minutes of mp3 music which that space can hold. For example, GB2min(1) = 940 is one test case.

hw02p, due Sep.05 (Tues)

Do the remaining problems with (exactly one) partner, as discussed in lecture and on the course-info sheet. Your functions below will be added to the class you've did for hw02i. You can choose one or the other of your previous solutions, or even a re-written version based on class discussion

1. (15pts, GB2albums)

   Write a function which takes as input a number of GB, and returns the number of entire albums which could entirely fit into that number of GB. (A plausible name for this function is GB2albums, but you are free to choose any reasonable name.) For example, 0.5GB might be enough space to store 10.6 albums; this means it can fit 10 albums entirely, so one test case might be GB2albums(0.5)=10. Therefore, the return type of this function should be int (but, see below).

   Use an estimate of 45min/album⁷. When writing test cases, you'll realize that you might need to round numbers down, since 100min is only enough to fit 2 complete albums. (No fractional albums!) Use the built-in function⁸ Math.floor to convert a fractional number to the nearest integer below it.

   Circumventing a 'possible loss of precision'

   Rather surprisingly, the number returned by Math.floor is not int, but is actually a double (albeit a double which will be as close to an int as it can be, like 123.000000000000, which implicitly suggests an accuracy of up to ±0.0000000000005.) This glitch is annoying; we'll discuss Java's rationale for this later, when we discuss Java's “nearly-guaranteed-correct” arithmetic).

   Two approaches are allowed for this homework, to overcome this glitch:

   • You can change GB2albums's return type to be double, and shake your head at Java's odd notion of Math.floor.
   • You can paste the following function into your code it has already been tested), and call it to convert types. (For this assignment, do not do casting yourself (aside from pasting the provided function); this homework is emphasizing function-call.)

     /* Given a double d, convert d's value to a nearby int; * whether this rounds up or down is unspecified. * WARNING: If d is outside of plus/minus 2.15billion (or so), * this program will crashsilently return a wildly incorrect answer! */ int double2int( double d ) { /* Turn d into an int by casting it. * (You can look up 'casting' in the book.) */ return (int) d; }

     If you do this, you'll shake your head at how you now have a program which lets you correctly appease Java's curiosity about types, but which will crash on certain inputs.

   Just so you know, there is a solution which really does return integers and won't ever crash; you can research classes java.math.BigInteger and java.math.BigDecimal if curious⁹

2. (15pts, GB2albumMessage) Write a function which takes as input a number of GB, and returns a String along the lines of¹⁰ "4GB should be enough to fit 23 albums.". You can name this function GB2albumMessage, or anything else reasonable.

   Remember that your function should return this string, and not print it to the screen using System.out.println.

3. (0pts) Reading from chapter 2: +Section 2.1 (Strings), +2.3 (primitive data types), + and +the first half of 2.4 (expressions, through Figure 2.4 (table of operator precedence)).

©2006, Ian Barland, Radford University

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu

Last modified 2006.Sep.05 (Tue)