Second Summer 2002

In this assignment you will be practicing with while and for loops.

First, write an algorithm to settle the following question:

A bank account starts out with $10,000. Interest is compounded at the end of every month at 6 percent per year (0.5 percent per month). At the beginning of every month, $500 is withdrawn to meet college expenses after the interest has been credited. After how many years is the account depleted?

Now suppose the numbers ($10,000, 6 percent, $500) were user-selectable. Are there values for which the algorithm you developed would not terminate? If so, make sure it always terminates.

Therefore you are to write a program that asks the user for three values:

• initial balance (a double)
• interest per year (another double, a percent value)
• monthly expenses (another double, in dollars)

frilled.cs.indiana.edu%java Interests
Welcome to the financial calculator.
What's your initial balance? 10000
What's the yearly interest? 6
How much do you plan to withdraw monthly? 500
The account will last 1 year(s) and 9 month(s).
Ending balance will be: 62.2 dollars.
frilled.cs.indiana.edu%java Interests
Welcome to the financial calculator.
What's your initial balance? 10000
What's the yearly interest? 6
How much do you plan to withdraw monthly? 100
The account will last 11 year(s) and 6 month(s).
Ending balance will be: 97.09 dollars.
frilled.cs.indiana.edu%java Interests
Welcome to the financial calculator.
What's your initial balance? 10000
What's the yearly interest? 6
How much do you plan to withdraw monthly? 10
This will last forever.
frilled.cs.indiana.edu%java Interests
Welcome to the financial calculator.
What's your initial balance? 10000
What's the yearly interest? 6
How much do you plan to withdraw monthly? 50
The account will last 525 year(s) and 1 month(s).
Ending balance will be: 48.1 dollars.
frilled.cs.indiana.edu%

Please call your program (the class) Interests for faster grading.

Do you see anything fishy in the examples given? (I hope you do.) What is it?

frilled.cs.indiana.edu%webster fishy
fishy \'fish-e^-\  fish-i-er; -est
(1547)
1: of or resembling fish esp. in taste or odor
2: creating doubt or suspicion: QUESTIONABLE 


frilled.cs.indiana.edu%

Here's the code used to produce the output above:

class Interests {
    public static void main(String[] args) {

	ConsoleReader c = new ConsoleReader(System.in); 

	System.out.println("Welcome to the financial calculator.");

	System.out.print("What's your initial balance? "); 
	double initialBalance = c.readDouble(); 

	System.out.print("What's the yearly interest? ");
	double yearlyInterest = c.readDouble() / 100; 

	System.out.print("How much do you plan to withdraw monthly? "); 
	double monthlyStipend = c.readDouble(); 

	double calculation = 
	    initialBalance * (1 + yearlyInterest / 12) - monthlyStipend; 

	if (calculation >= initialBalance) {
	    System.out.println("This will last forever."); 

	} else {

	    double balance = initialBalance; 

	    int months = 0; 

	    while (balance * ( 1 + yearlyInterest / 12) > monthlyStipend) {
		months += 1; 
		balance = balance * (1 + yearlyInterest / 12) - monthlyStipend;
	    }

	    int years = months / 12; 
	    months = months % 12; 

	    System.out.println("The account will last " + years + 
			       " year(s) and " + months + " month(s)."); 

	    System.out.println("Ending balance will be: " + 
			       Math.round(balance * 100) / 100.00
			       + " dollars."
			       ); 

	}

    }
}