Homework Assignment 3

Due: 9am, November 2, 2007.

This assignment will give you practice at writing Java programs where:

Input is read from the keyboard, and
Branching and looping constructs are used in the solution of simple engineering problems.
Program output is organized into a tidy table.

Click here to download the pdf file of questions.

A few hints. Most of what you need can be found on the "java examples" web page and in the green class reader:

In past years, we have employed the method keyboardInput() to read input typed at the keyboard. Now that Java 5 is available, you should replace the method keyboardInput() with getTextFromConsole().
Solutions to a number of the problems in "java exercises" can be found in the purple book. You should look at them to see how your program should be structured, what packages need to be included, and so forth.

It is important to organize your data and methods correctly. Here is a suggested program layout for problem 1.

/*
 *  ==================================================================
 *  FourNumbers.java: Prompt user for four floating point numbers,
 *  print each number, and then the smallest and largest values.
 *  ==================================================================
 */

import java.lang.Math;
import java.io.*;

public class FourNumbers {
    public static void main( String args[] ) {
        double dA, dB, dC, dD;
        String sLine;

        // Prompt user for numbers dA, dB, and dC.

        .... details removed ....

        System.out.println("Please enter dA, dB, dC and dD");

        .... details removed ....

        // Print each of the numbers ....

        .... details removed ....

        // Ccmpute and print largest/smallest values....

        .... details removed ....

    }

    /* 
     *  ============================================================
     *  Method getTextFromConsole(): Read line of text from keyboard
     * 
     *  Input  : None.
     *  Output : String sLine -- character string of keyboard input
     *  ============================================================
     */

    public static String getTextFromConsole() {
       String inLine = "";

       ... get details from java examples web page ....

       return inLine;
    }
}

The program source code will be contained in a file called FourNumbers.java. Source code for the FourNumbers class will contained two user-defined methods: main() and getTextFromConsole().

In the third problem, the loop covers the range -4 through 10 in increments of 0.2. Error conditions will occur when x equals 2 (divide by zero) and the denominator of x/sin(x) equals zero (i.e., x = 0). Two approaches to this problem make sense.
Option 1. You can test for an error before it happens (i.e., x = 0 and x = 2). Unfortunately, the increment of 0.2 cannot be stored exactly inside a computer, so the looping construct will not walk along the sequence
```
    -4.0 -3.8 -3.6 .... 9.8 10.0
```
exactly. So instead of writing something like:
```
    if ( dX == 0 ) {
         ... print appropriate error message ...
    }
    if ( dX == 2 ) {
         ... print appropriate error message ...
    }
```
you should construct your test around a tolerance, e.g.,
```
    if ( Math.abs(dX-2.0) < 0.000005 ) {
         ... print appropriate error message ...
    }
```
Option 2. Ignore the fact that errors in y(x) will occur, and simply adjust your output according to the following outcomes: (1) y(x) results in a number (no problem!), (2) y(x) causes an overflow (Infinity), (3) y(x) causes an underflow (-Infinity), and (4) y(x) evaluates to something that isn't a number (NaN). For a hint on a suitable coding strategy, see the Numerical Error Conditions code on the java examples page.

Note. For each problem, hand in a copy of your program source code and a script of I/O for typical program usage. To create a script, type something like:

    prompt >> script output-file

Now all input/output on the screen will be echoed to the file "output-file". To terminate the script, type:

    prompt >> exit

Now print "output-file" and hand it in.