Homework Assignment 3

Due: 9am, April 1, 2009.

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

Input is read from the keyboard,
Output is formatted into a tidy table.
Where Math functions are evaluated via calls to methods in the Math library (e.g., Math.max(), Math.min() and Math.sqrt()).
A user-defined function computes the factorial of a number (e.g., 3! = 6).

Solve problems 2, 3, and 5 in the Java Programming Exercises.

A few hints. Most of what you need can be found on the "java examples" web page and in the blue 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 class reader. 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 4.

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

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

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

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

        .... details removed ....

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

        .... 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;
    }
}

Notice that the source code for the method getTextFromConsole() needs to be "inside" the class ThreeNumbers.

Here is an abbreviated solution to the four-fours problem.
The Math package does not have a factorial function -- and I am not sure why -- so you'll need a user-defined method.

import java.lang.Math;

public class FourFours {

    // =============================================
    // Compute and return iNo !
    // =============================================

    public static int factorial( int iNo ) {

        // Make sure that the input argument is positive

        if (iNo < 0) throw
           new IllegalArgumentException("iNo must be >= 0");

        // Use simple look to compute factorial....

        int factorial = 1;
        for(int i = 2; i <= iNo; i++)
            factorial *= i;

        return factorial;
    }

    // ==================================================
    // Compute and print expressions involving four fours
    // ==================================================

    public static void main ( String args[] ) {

       System.out.printf("\n");
       System.out.printf("Expressions involving four fours                \n");
       System.out.printf("================================================\n");

       System.out.printf("Four fours:  0 = %10d\n",  4/4 - 4/4 );
       System.out.printf("Four fours:  1 = %10d\n",  44/44 );

       // .... etc ..... etc ......

       System.out.printf("================================================\n");
    }
}

The output to my solution looks like:

Expressions involving four fours                
================================================
Four fours:  0 =          0
Four fours:  1 =          1
Four fours:  2 =          2
Four fours:  3 =          3
Four fours:  4 =          4
Four fours:  5 =          5
Four fours:  6 =          6
Four fours:  7 =          7
Four fours:  8 =          8
Four fours:  9 =          9
Four fours: 10 =         10
Four fours: 11 =         11
Four fours: 12 =         12
Four fours: 13 =         13
Four fours: 14 =         14
Four fours: 15 =         15
Four fours: 16 =         16
Four fours: 17 =         17
Four fours: 18 =         18
Four fours: 19 =         19
... and ... 
Four fours: 73 =         73
================================================

Note. For each problem, hand in a copy of your program source code and a script of I/O for typical program usage.

If you are working on UNIX/Mac OS X then the procedure for creating a script is easy -- just 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.

If you are working on Windows, just cut-and-paste the output into a Word document.