Develop Reference

Why is my while loop printing out the same thing each time?

I'm sorry, I know this question is probably asked a million different times every day, but I truly can't find the answer I'm looking for. I'm a beginner in Java (I'm in college and learning a bunch of new languages), and my while loop is printing out the same thing every time.
import java.util.Scanner;
public class Main
{
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.println("What is the loan amount? ");
int amount = scanner.nextInt();
int x = 1;
//your code goes here
while (x < 6){
System.out.println("Month " +x+ ":");
int percent = (amount / 10);
System.out.println("Payment: 10 percent of " +amount+ " = " +percent);
int rAmt = amount - percent;
System.out.println("Remaining amount: " +rAmt);
x++;
}
}
}

So the issue is that you never actually change amount after doing your calculations inside the while loop. What I think you want to do, is to set amount = rAmt;, which would produce the following code. This will cause the amount to be decreased by 10% each iteration, and this new value carried forward.
...
//your code goes here
while (x < 6){
System.out.println("Month " +x+ ":");
int percent = (amount / 10);
System.out.println("Payment: 10 percent of " +amount+ " = " +percent);
int rAmt = amount - percent;
System.out.println("Remaining amount: " +rAmt);
amount = rAmt;
x++;
}
...

How to show all iterations of a loop, within a single message box?

Everything is working properly, no logic or syntax errors, however, I need the code at the end to display a single message box that shows all iterations at once like a table, as opposed to having x amount of message boxes pop up with results. I'm not sure how to go about it, the only similar examples in my textbook don't use message boxes.
import java.text.DecimalFormat;
import javax.swing.JOptionPane;
public class PenniesForPay
{
public static void main(String[] args)
{
int days;
int maxDays;
double pay = 0.01;
double totalPay; //accumulator
String input;
//Decimal Format Object to format output
DecimalFormat dollar = new DecimalFormat("#,##0.00");
//Get number of days
input = JOptionPane.showInputDialog("How many days did you work?");
maxDays = Integer.parseInt(input);
//Validate days
while (maxDays < 1)
{
input = JOptionPane.showInputDialog("The number of days must be at least one");
days = Integer.parseInt(input);
}
//Set accumulator to 0
totalPay = 0.0;
//Display Table
for (days = 1; days <= maxDays; days++)
{
pay *= 2;
totalPay += pay; //add pay to totalPay
// NEEDS TO SHOW ALL ITERATIONS IN SINGLE MESSAGE BOX
JOptionPane.showMessageDialog(null,"Day " + " Pay" + "\n----------------\n" +
days + " $" + pay + "\n----------------\n" +
"Total Pay For Period: $" + dollar.format(totalPay));
}
//terminate program
System.exit(0);
}
}

You can use a StringBuilder to accumulate all the messages, and then display them, once, after the loop is done:
StringBuilder sb = new StringBuilder();
for (days = 1; days <= maxDays; days++) {
pay *= 2;
totalPay += pay; //add pay to totalPay
sb.append("Day Pay\n----------------\n")
.append(days)
.append(" $")
.append(pay)
.append("\n----------------\n")
.append("Total Pay For Period: $")
.append(dollar.format(totalPay));
}
JOptionPane.showMessageDialog(sb.toString());

Use your JOptionPane.showMessageDialog outside the for loop. Use StringBuffer or StringBuilder to append your messages and show at once.

java loop to repeat program

I am extremely new to java I am in my second week in classes or so--
I need my program to keep going or exit according to the user. It is a payroll calculation and I want the end to say "Do you want to continue (y/n)" I want Y to repeat my entire program of questions and no to end program. I am using Jgrasp and I am very very new. I am assuming it needs a loop and I am not totally sure, I just got this to run and compile correctly-- it runs correctly for me so it is a good start and I am hoping to get help on how to do this as I am seeing a ton of different ways and different programs for it. thanks.
import java.util.Scanner;
public class calculations {
public static void main(String [] args) {
Scanner reader = new Scanner(System.in);
Scanner in = new Scanner(System.in);
double Regpay;
double Payperhour;
int HoursAweek;
double Pay;
double OvertimeHours;
double OvertimePay;
double Dependants;
double SocSecTax;
double FederalTax;
double StateTax;
int UnionDues;
double AllTaxes;
double FinalPay;
String playAgain;
System.out.print("Enter your pay per hour:");
Payperhour = reader.nextDouble ();
System.out.print("Enter your regular Hours a week:");
HoursAweek = reader.nextInt();
System.out.print("Enter your overtime hours:");
OvertimeHours = reader.nextDouble();
Regpay = Payperhour * HoursAweek;
OvertimePay = OvertimeHours * 1.5 * Payperhour;
Pay = OvertimePay + Regpay;
SocSecTax = Pay * .06;
FederalTax = Pay * .14;
StateTax = Pay * .05;
UnionDues = 10;
AllTaxes = SocSecTax + FederalTax + StateTax + UnionDues;
FinalPay = Pay -= AllTaxes;
System.out.println("Your pay this week will be " +FinalPay);
{
System.out.println("How many Dependants:");
Dependants = reader.nextInt();
if (Dependants >= 3) {
Dependants = Pay + 35;
System.out.println("Your Pay is:" +Dependants);
} else if(Dependants < 3) {
System.out.println("Your Pay is:" +Pay);
}
}
}
}

Here is the basic idea with your code:
import java.util.Scanner;
public class calculations{
public static void main(String [] args) {
Scanner reader = new Scanner(System.in);
Scanner in = new Scanner(System.in);
double Regpay;
double Payperhour;
int HoursAweek;
double Pay;
double OvertimeHours;
double OvertimePay;
double Dependants;
double SocSecTax;
double FederalTax;
double StateTax;
int UnionDues;
double AllTaxes;
double FinalPay;
String playAgain;
int runAgain = 1;
while (runAgain == 1) {
System.out.print("Enter your pay per hour:");
Payperhour = reader.nextDouble();
System.out.print("Enter your regular Hours a week:");
HoursAweek = reader.nextInt();
System.out.print("Enter your overtime hours:");
OvertimeHours = reader.nextDouble();
Regpay = Payperhour * HoursAweek;
OvertimePay = OvertimeHours * 1.5 * Payperhour;
Pay = OvertimePay + Regpay;
SocSecTax = Pay * .06;
FederalTax = Pay * .14;
StateTax = Pay * .05;
UnionDues = 10;
AllTaxes = SocSecTax + FederalTax + StateTax + UnionDues;
FinalPay = Pay -= AllTaxes;
System.out.println("Your pay this week will be " + FinalPay);
{
System.out.println("How many Dependants:");
Dependants = reader.nextInt();
if (Dependants >= 3) {
Dependants = Pay + 35;
System.out.println("Your Pay is:" + Dependants);
} else if (Dependants < 3) {
System.out.println("Your Pay is:" + Pay);
}
}
System.out.println("Again??? Press 1 to run again and 0 to exit");
runAgain = reader.nextInt();
}
}
}

Here's a guide for you..
You can create a method for the transaction.
//Place this on your main method
do{
//call the method
transaction();
//ask if the user wants to repeat the program
System.out.print("Do you want to continue (y/n)");
input = reader.nextLine();
}while(input.equalsIgnoreCase("Y"))
public void transaction(){
//your transaction code here..
}

Here is a brief idea of how to do this:
String choice = "y";
while(true) {
//Take input
System.out.print("Do you want to continue (y/n)?");
choice = reader.nextLine();
if(choice.equalsIgnoreCase("n")) break;
//else do your work.
}
You can also sue do-while to get what you want. You may need to make some changes but then that is the entire idea. It is just a hint.

compound interest after 1, 3 and 5 years

i have this code that calculates the compound interest, but i need it to do it for after 1, 3, and 5 years. ive tried and cant seem to get it to work. can anyone help me?
import java.util.Scanner;
public class CompoundInterest {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
double principal = 0;
double rate = 0;
double time = 0;
double x = 0;
System.out.print("Enter the amount invested : ");
principal = input.nextDouble();
System.out.print("Enter the Rate of interest : ");
rate = input.nextDouble();
System.out.print("Enter the Time of loan : ");
time = input.nextDouble();
x = principal * Math.pow((1 + rate/12),time);
x = Math.pow(5,3);
System.out.println("");
System.out.println("The Compound Interest after 1 year is : "
+ x);
}
}

Why do you set x to principal *((1+r/12),time), then set x=math.pow(5,3)?
x is now set to math.pow(5,3) and has nothing to do with your inputs of principal, rate, and time.
Also, you should specify that the time input is years, as you have that hard coded in the rate question.

return issue for method

I am having an issue with a method returning to the main method. It is saying that amount in "return amount" cannot be resolved to a variable. Where am I off on this??
This is the message I get:
Multiple markers at this line
- Void methods cannot return a
value
- amount cannot be resolved to a
variable
Here is the code:
import java.util.Scanner;
public class Investment {
public static void main(String[]args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the amount invested: ");
double amount = input.nextDouble();
System.out.print("Enter the annual interest rate: ");
double interest = input.nextDouble();
int years = 30;
System.out.print(futureInvestmentValue(amount, interest, years)); //Enter output for table
}
public static double futureInvestmentValue(double amount, double interest, int years) {
double monthlyInterest = interest/1200;
double temp;
double count = 1;
while (count < years)
temp = amount * (Math.pow(1 + monthlyInterest,years *12));
amount = temp;
System.out.print((count + 1) + " " + temp);
}
{
return amount;
}
}

You curly braces are not correct. The compiler - and me - was confused about that.
This should work (at least syntactically):
import java.util.Scanner;
public class Investment {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the amount invested: ");
double amount = input.nextDouble();
System.out.print("Enter the annual interest rate: ");
double interest = input.nextDouble();
int years = 30;
System.out.print(futureInvestmentValue(amount, interest, years));
}
public static double futureInvestmentValue(
double amount, double interest, int years) {
double monthlyInterest = interest / 1200;
double temp = 0;
double count = 1;
while (count < years)
temp = amount * (Math.pow(1 + monthlyInterest, years * 12));
amount = temp;
System.out.print((count + 1) + " " + temp);
return amount;
}
}

Remove amount from its own scope As a start. Also from the method futureInvestmentValue, you take in amount as an argument but the value is never modified so you're returning the same value being passed which is most likely not the desired outcome.

remove return amount from its own scope
the method futureInvestmentValue... You can't modify any of the parameters inside the method so you have to declare another variable besides amount inside the method (maybe it's the temp variable you keep using) and return that instead
when you return something, the return statement is always inside the method. Never outside it while inside its own braces (never seen this before...)
import java.util.Scanner;
public class Investment {
public static void main(String[]args) {
Scanner input = new Scanner(System.in);
System.out.print("Enter the amount invested: ");
double amount = input.nextDouble();
System.out.print("Enter the annual interest rate: ");
double interest = input.nextDouble();
int years = 30;
System.out.print(futureInvestmentValue(amount, interest, years)); //Enter output for table
}
public static double futureInvestmentValue(double amount, double interest, int years) {
double monthlyInterest = interest/1200;
double temp;
double count = 1;
while (count < years) {
temp = amount * (Math.pow(1 + monthlyInterest,years *12));
System.out.print((count + 1) + " " + temp);
}
return amount;
}
}