Thread: Factorial Test Program

This is a homework assignment that have been unable to complete. I've been working on it for 6 days with no success. Everything I try causes the code to fail.

The code I'm working on is a test program to run against this code.

// method factorial
// computes the factorial for 01 to 12! using a table lookup
// factorials larger than 12! exceed the largest value that can be stored
// in a Java primitive integer
public class Factorial
{
	public static int factorial(int n)
	{
		final int f[] = { 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880, 3628800, 39916800, 479001600};
		return f[n];
	}
}

The test program needs to catch any exceptions that occur so the program doesn't terminate. The number range is factorials for 0 through 12 only. If the user enters a negative number, a number higher than 12, blank, special characters, or alphabet the exception should be handled.

import java.util.InputMismatchException;
import java.util.Scanner;
 
public class FactorialTest
{
	public static void main (String args[])
	{
		Factorial f = new Factorial();
 
		// create scanner object to read user input
		Scanner scanner = new Scanner(System.in);
 
		// prompt user to enter a number between 0 and 12
		System.out.println("Please enter a number between 0 and 12");
 
		// store value entered by user
		int n = scanner.nextInt();
 
		// assert the value of n is between 0 and 12
		assert (n >= 0 && n <= 12);
 
		System.out.println("Factorial of "+n+" is = "+f+"");
		try
		{
		}	
			catch (InputMismatchException inputMismatchException)
			{
				System.err.printf("/nException: %s\n", inputMismatchException);
				scanner.nextLine(); // discard input so user can try again
				System.out.println("You must enter a number between 0 and 12");
			}
 
		if (n < 0)
			System.out.println("Number should be non-negative.");
		else
		{
			for (n = 0; n <= 12; n++);
 
		}	
	}
}

I checked with my college campus but they do not have any tutors to help with Java programming. I also contacted my instructor but he is not available on weekends. This assignment is due on 2/23/2014.

The final output needs to look something like this:

Enter an integer number: abc
You must enter an integer - please re-enter:
Enter an integer number: -5
Factorial of this value cannot be represented as an integer.
Please re-enter your integer:
Enter an integer number: 13
Factorial of this value cannot be represented as an integer.
Please re-enter your integer:
Enter an integer number: 9
The factorial of 9 is 362880.
Done!


Output when a letter is entered
Please enter a number between 0 and 12
a
Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at FactorialTest.main(FactorialTest.java:25)

Output when a number between 0 and 12 is entered
Please enter a number between 0 and 12
8
Factorial of 8 is = Factorial@171bbc9

Output when a negative number is entered
Factorial of -9 is = Factorial@6f7ce9
Number should be non-negative.

The program is not working the way I need it to. When a number between 0 and 12 is entered the factorial amount should be pulled from main program and display in the output but it isn't
When a negative number is entered the output should only display "Number should be non-negative" and allow the user to enter another number.
When a letter is entered the output should display " Please enter a number between 0 and 12" and allow the user to enter another number.

Any assistance you can provide on what I'm doing wrong is greatly appreciated.


phendrickson

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Thank you for your help, I added the try-catch but the program is not working the way I need it to.

The final output needs to look like this:

Enter an integer number: abc
You must enter an integer - please re-enter:
Enter an integer number: -5
Factorial of this value cannot be represented as an integer.
Please re-enter your integer:
Enter an integer number: 13
Factorial of this value cannot be represented as an integer.
Please re-enter your integer:
Enter an integer number: 9
The factorial of 9 is 362880.
Done!

When a letter is entered the output should display " Please enter a number between 0 and 12" and allow the user to enter another number.
Instead this is the output I get

Please enter a number between 0 and 12
a
Exception in thread "main" java.util.InputMismatchException
at java.util.Scanner.throwFor(Unknown Source)
at java.util.Scanner.next(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at java.util.Scanner.nextInt(Unknown Source)
at FactorialTest.main(FactorialTest.java:25)

When a number between 0 and 12 is entered the factorial amount should be pulled from the main program and display in the output but it isn't, instead the is what my output looks like.

Please enter a number between 0 and 12
8
Factorial of 8 is = Factorial@171bbc9

When a negative number is entered the output should only display "Number should be non-negative" and allow the user to enter another number.
Instead, this is the output I'm getting.

Factorial of -9 is = Factorial@6f7ce9
Number should be non-negative.