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trouble with while loop java

This is extremely simple and I'm sorry I am having trouble getting this to work. It works when I remove the while loop with just the processing, but I'm not sure what I'm doing wrong with the whileloop. Any suggestions?
/*Cobalt
60, a radioactive form of cobalt used in cancer therapy, decays or
dissipates over a period of time. Each year, 12 percent of the
amount present at the beginning of the year will have decayed. If
a container of cobalt 60 initially contains 10 grams, create a
Java program to determine the amount remaining after five years. */
public class Cobalt {
public static void main(String[] args) {
//dec
double CInitial = 10.0;
double decay = .12;
double CUpdatedA, CUpdatedB;
//proc
int years = 0;
while (years < 5);
{
CUpdatedA = CInitial * decay;
CUpdatedB = CInitial - CUpdatedA;
years++;
}
//out
System.out.println("the amount of cobalt left after 5 years is"
+ CUpdatedB);
}
}

In your code, read this line carefully :
while (years < 5);
There is a semicolon at the end, which means that this statement is finished.
You might ask, "why doesn't the bracket cause an error?"
The brackets mean a section, it does not affect the code.
The way to make this work is to remove the colon.
ALSO,
You need to initiailize your variables or the compilers will show
variable CUpdatedB might not have been initialized
(write CUpdatedA, CUpdatedB = 0)

Besides, the while loop issue i.e, removing of semicolon. You don't seem to be getting correct answer because at the end of every loop your CInitial is not updated with the value after decay during that year.
Here am resetting CInitial with CUpdatedB as a last statement in while loop.
public class Cobalt {
public static void main(String[] args) {
//dec
double CInitial = 10.0;
double decay = 0.12;
double CUpdatedA = 0, CUpdatedB = 0;
//proc
int years = 0;
while (years < 5)
{
CUpdatedA = CInitial * decay;
CUpdatedB = CInitial - CUpdatedA;
CInitial = CUpdatedB;
years++;
}
//out
System.out.println("the amount of cobalt left after 5 years is: " + CUpdatedB);
}
}
Output: the amount of cobalt left after 5 years is: 5.277319168
I hope thats the answer your expecting.

How can I turn this compound value function into a for-loop?

Okay so I am new to Java. I have a program that calculates the compound value after asking the user for a savings amount and an annual interest rate. I'm having trouble getting it into a for loop but I feel like I'm somewhat close? The hard part in my mind is understanding how to get the last months total into the new calculation.
Here's my formula for the compound value currently:
firstMonth = savingAmount * (1 + monthlyInterestRate);
secondMonth = (savingAmount + firstMonth) * (1 + monthlyInterestRate);
thirdMonth = (savingAmount + secondMonth) * (1 + monthlyInterestRate);
fourthMonth = (savingAmount + thirdMonth) * (1 + monthlyInterestRate);
fifthMonth = (savingAmount + fourthMonth) * (1 + monthlyInterestRate);
sixthMonth = (savingAmount + fifthMonth) * (1 + monthlyInterestRate);
It is ugly obviously and it should be in a for-loop. Again the savingAmount is user input and the annualInterestRate is user input. The the monthlyInterestRate is annualInterestRate/12.
Here is the for-loop I have so far.
for (int i = 1; i <= 6; i++ );
{
sixthMonth = savingAmount * Math.pow(1+monthlyInterestRate, 6);
}
I am still learning for-loops but doesn't my code say it adds up while it is less than or equal to 6? And while those are true to do the formula I provided. No you don't have to answer the question but if you could lead me in the right direction that'd be great. So how would I start to convert it? Feel free to ask for more info if needed.

Try this:
for (int i = 1; i <= 6; i++) {
monthAmount = (savingAmount + monthAmount) * (1 + monthlyInterestRate);
}
This should get you to the same answer.
You were on the right track, but this will allow you to use the previous months amount in the formula. This code will also work for however long you want the loop to run for.

I would actually recommend using the compound interest formula A = P (1 + r/n) ^ nt.
A - final amount with compound growth
P - principal investment
r - annual interest rate
n - number of times the interest is compounded per time period
t - number of time periods compounded
So you could then reduce all of this to:
amount = savingAmount * Math.pow(1 + monthlyInterestRate/timesCompoundedPerMonth,
timesCompoundedPerMonth * monthsCompounded);
Compound Interest Formula - Explained

I would recommending storing the amounts in a list for easy lookup if you want to see how much savings you will have at each month.
public static void main(String args[]) {
double savingsAmount = 543.23;
double annualInterestRate = 0.85; // %
double monthlyInterestRate = annualInterestRate / 12;
List<Double> savings = new ArrayList<Double>();
savings.add(savingsAmount); // month 0
int monthsInTheFuture = 6;
double compoundInterest = 1 + monthlyInterestRate;
for (int i = 1; i <= monthsInTheFuture; i++) {
double previousSavings = savings.get(i-1);
double nextSavings = previousSavings * compoundInterest;
savings.add(nextSavings);
}
System.out.println(savings);
}

java compound interest with contributions formula

I am currently trying to develop a compound interest calculator that includes monthly contributions. I have successfully been able to get the compound interest calculation working without the monthly contributions using the following line of code, but cannot figure out what the formula should be when adding monthly contributions.
double calculatedValue = (principalValue * Math.pow(1 + (interestRateValue/numberOfCompoundsValue), (termValue * numberOfCompoundsValue)));
When trying to get the calculated value with contributions I changed the way this is done. See the following code how I approached this.
//The starting principal
double principalValue = 5000;
//Interest rate (%)
double interestRateValue = 0.05;
//How many times a year to add interest
int numberOfCompoundsValue = 4;
//The number of years used for the calculation
double termValue = 30;
//The monthly contribution amount
double monthlyContributionsValue = 400;
//How often interest is added. E.g. Every 3 months if adding interest 4 times in a year
int interestAddedEveryXMonths = 12/numberOfCompoundsValue;
//The total number of months for the calculation
int totalNumberOfMonths = (int)(12 * termValue);
for(int i = 1; i <= totalNumberOfMonths; i++)
{
principalValue += monthlyContributionsValue;
if(i % interestAddedEveryXMonths == 0)
{
principalValue += (principalValue * interestRateValue);
}
}
I figured this should do what I am after. Every month increase the principal by the contribution amount and if that month equals a month where interest should be added then calculate the interest * the interest rate and add that to the principal.
When using the values above I expect the answer $355,242.18 but get $10511941.97, which looks better in my bank account but not in my calculation.
If anyone can offer me some help or point out where I have gone wrong that would be much appreciated.
Thanks in advance

Your problem is here:
principalValue += (principalValue * interestRateValue);
You're adding a full year's interest every quarter, when you should be adding just a quarter's interest. You need to scale that interest rate down to get the right rate.
Here's an example:
class CashFlow {
private final double initialDeposit;
private final double rate;
private final int years;
private final double monthlyContribution;
private final int interestFrequency;
CashFlow(double initialDeposit, double rate, int years,
double monthlyContribution, int interestFrequency) {
if ( years < 1 ) {
throw new IllegalArgumentException("years must be at least 1");
}
if ( rate <= 0 ) {
throw new IllegalArgumentException("rate must be positive");
}
if ( 12 % interestFrequency != 0 ) {
throw new IllegalArgumentException("frequency must divide 12");
}
this.initialDeposit = initialDeposit;
this.rate = rate;
this.years = years;
this.monthlyContribution = monthlyContribution;
this.interestFrequency = interestFrequency;
}
public double terminalValue() {
final int interestPeriod = 12 / interestFrequency;
final double pRate = Math.pow(1 + rate, 1.0 / interestPeriod) - 1;
double value = initialDeposit;
for ( int i = 0; i < years * 12; ++i ) {
value += monthlyContribution;
if ( i % interestFrequency == interestFrequency - 1 ) {
value *= 1 + pRate;
}
}
return value;
}
}
class CompoundCalc {
public static void main(String[] args) {
CashFlow cf = new CashFlow(5000, 0.05, 30, 400, 3);
System.out.println("Terminal value: " + cf.terminalValue());
}
}
with output:
run:
Terminal value: 350421.2302849443
BUILD SUCCESSFUL (total time: 0 seconds)
which is close to the $355k value you found.
There are a number of different conventions you could use to get the quarterly rate. Dividing the annual rate by 4 is a simple and practical one, but the pow(1 + rate, 1 / 4) - 1 method above is more theoretically sound, since it's mathematically equivalent to the corresponding annual rate.

After some brief testing I've come to the conclusion that either you have:
miscalculated the value you want ($355,242.18)
OR
incorrectly asked your question
The calculation you've described that you want ($5000 start + $400 monthly contributions for 30 years + interest every 3 months) is found by the code you've provided. The value that it gives ($10,511,941.97) is indeed correct from what I can see. The only other suggestions I can offer are to only use double if you need to (for example termValue can be an int) AND when ever you know the value is not going to change (for example interestRateValue) use final. It will help avoid any unforeseen error in larger programs. I hope this helps you figure out your interest calculator or answers any questions you have.

static void Main(string[] args)
{
double monthlyDeposit;
double rateOfInterest;
double numberOfCompounds;
double years;
double futureValue = 0;
double totalAmount = 0;
Console.WriteLine("Compound Interest Calculation based on monthly deposits");
Console.WriteLine("Monthly Deposit");
monthlyDeposit = Convert.ToDouble(Console.ReadLine());
Console.WriteLine("Rate Of Interest");
rateOfInterest = Convert.ToDouble(Console.ReadLine());
Console.WriteLine("Number of Compounds in a year");
numberOfCompounds = Convert.ToDouble(Console.ReadLine());
Console.WriteLine("Number of year");
years = Convert.ToDouble(Console.ReadLine());
futureValue = monthlyDeposit;
for (int i = 1; i <= years * 12; i++)
{
totalAmount = futureValue * (1 + (rateOfInterest / 100) / 12);
if (i == years * 12)
futureValue = totalAmount;
else
futureValue = totalAmount + monthlyDeposit;
}
Console.WriteLine("Future Value is=" + futureValue);
Console.ReadLine();
}
//Output
Compound Interest Calculation based on monthly Deposits
Monthly Deposit
1500
Rate Of Interest
7.5
Number of Compounds in a year
12
Number of year
1
Future Value is=18748.2726237313

Java - calculating total with cost and unknown number of items

I have a task here: Define a class PayPerView with method moviefee() that calculates the monthly charges for movies rented. The method should take one argument representing number of movies rented and return the fee as a double.
The rental fee fee is $6.99 per movie. Preferred customers that rent more than 10 per month get a discount of 5%.
Here's my code so far:
public class PayPerView {
public static void main(String [] args){
}
public static double moviefee(int n){
double fee = 6.99;
double total= n*fee;
System.out.println("Your balance due this month is" + total);
//return 6.99*n * ((n>10) ? 0.95:1);
}}
I know it's awful, I'm sorry and you can ignore that last line of code I commented out because I'm going to redo it and turn it into an if statement. I thought maybe I should use an array, but I can't right? Because I don't know how many movies are/will be rented? Should I use an arraylist for the number of movies rented?

Actually that line you commented out looks pretty much exactly what you are trying to do anyway. Is there something particularly wrong with it?
If you really need to output the result on the console...
final double fee = 6.99;
double total = n * fee * (n > 10 ? .95 : 1.0);
System.out.println("Your balance due this month is" + total);
return total;

I don't see why you'd use an ArrayList if you don't have any data to put into it.
You'd probably want to try something along these lines:
double total = n * fee;
if (n > 10) {
total *= 0.95;
}
I also see that you wanted to use the ternary operator, so you could replace the above code block with
double total = n * fee * (n > 10 ? 0.95 : 1.0);

Your on the right track
public static double moviefee(int n){
double fee = 6.99;
double total;
if(n <= 10){
total= n*fee;
}
else{
total= n*fee - (n*fee*0.05); //5 percent discount
}
System.out.println("Your balance due this month is" + total);
return total;
}
Edit: added double total;

calculating interest on a certificate of deposit

I'm working on a program that will calculate the basic interest accrued on a certificate of deposit. The program asks for the amount of money invested and the term (up to five years). Depending on how many years their term is, is what determines how much interest is earned. I use an if/else statement to determine the rate of interest. I then use a loop to print out how much money is in the account at the end of each year. My problem is that when I run the program, the money is not counting.
Here is the entire code.
import java.util.Scanner;
public class CDCalc
{
public static void main(String args[])
{
int Count = 0;
double Rate = 0;
double Total = 0;
Scanner userInput = new Scanner(System.in);
System.out.println("How much money do you want to invest?");
int Invest = userInput.nextInt();
System.out.println("How many years will your term be?");
int Term = userInput.nextInt();
System.out.println("Investing: " + Invest);
System.out.println(" Term: " + Term);
if (Term <= 1)
{
Rate = .3;
}
else if (Term <= 2)
{
Rate = .45;
}
else if (Term <= 3)
{
Rate = .95;
}
else if (Term <= 4)
{
Rate = 1.5;
}
else if (Term <= 5)
{
Rate = 1.8;
}
int count = 1;
while(count <= 5)
{
Total = Invest + (Invest * (Rate) / (100.0));
System.out.println("Value after year " + count + ": " + Total);
count++;
}
}
}
and here is the result I get with a 10 dollar investment, just to keep it simple, and a 5 year investment.
How much money do you want to invest?
10
How many years will your term be?
5
Investing: 10
Term: 5
Value after year 1: 10.18
Value after year 2: 10.18
Value after year 3: 10.18
Value after year 4: 10.18
Value after year 5: 10.18
My main problem is I dont know how to make it continually add the intrest onto the total. I'm not sure if I need to use a different loop or what. Any help would be appreciated.

Total = Invest + (Invest * (Rate) / (100.0));
You are not changing the value of Invest for each year, so it is not compounding. It is like you are getting .18$ of interest each year, retired from the account.
Change Total for Invest.

You need to add the investment interest to your total:
Total = Invest;
int count = 1;
while(count <= 5)
{
Total = Total + (Invest * (Rate) / (100.0));
System.out.println("Value after year " + count + ": " + Total);
count++;
}