Develop Reference

Compound interest

import java.util.*;
public class Project3{
public static void main(String[] args)
{
Scanner key = new Scanner (System.in);
double rate = 0.05;
double annually, monthly, daily;
double balance;
int year = 10 ;
System.out.println("Enter the amount you will like to deposit or type exit to end.");
int deposit = key.nextInt();
annually = deposit * Math.pow((1 + rate/1),year);
monthly = deposit * Math.pow((1 + rate/12),year);
daily = deposit * Math.pow((1 + rate/365),year);
while (deposit)
{
}
System.out.println(annually);
System.out.println(monthly);
System.out.println(daily);
}
}
This is what I currently have. What I am trying to accomplish is to make a loop to add the first outcome with the next one. Also make one formula instead of having three to find the annually, monthly and daily.

First and foremost, asking someone to write out your homework is really unethical, and not helpful for you in the long run. If you don't care about the long run, consider taking a different class. In a career scenario, you're expected to write code on your own.
Secondly, to actually answer your question, here are some tips:
It seems like you want to gather a value (deposit) from the user, and then calculate the Compound Interest for said value. Your program also needs to not exit until the user says to exit. i.e. they want to calculate the CI for a set of numbers.
First step is to check the value from the user. If it is a number, then do calculations on it. If it is a String, then check if it is "exit". In Java, this amounts to writing out an if-statement, and making use of the very helpful "instanceof" keyword. If you haven't learned about that, give this a read, or ask your teacher.
For the calculations part, you simply do calculations on the user's input while the input is not a string set to "exit".
Finally, print out your calculations.
That's it. Your code already has the calculation formulas down, so you just need to code the logic for handling user input.

import java.util.Scanner;
import java.lang.Math;
public class HelloWorld {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.println("How much money you want to deposit?");
int principle = sc.nextInt();
System.out.println("what is the rate you want?");
float rate = sc.nextFloat();
System.out.println("After how many years, you want to see your money?");
int year = sc.nextInt();
System.out.println("How many compounds in a year?");
int partialTime = sc.nextInt();
double b = year * partialTime;
double a = 1 + (rate/(partialTime*100));
double x = principle * (Math.pow(a,b));
System.out.println("Your interest in given time would be " + x);
}
}

A couple of suggestions - since you want to check user input against both String and int types, you could define a String type variable to hold the user input, and then do a try/catch to parse it as an Integer, if it's not an Integer check if the input equals "exit" (using the String.equals() method).
import java.util.*;
public class Project3{
public static void main(String[] args)
{
Scanner key = new Scanner (System.in);
double rate = 0.05;
double annually = 0, monthly = 0, daily = 0;
double balance;
int year = 10, deposit = 0 ;
String userinput = "";
do {
try {
System.out.println("Enter the amount you will like to deposit or type exit to end.");
userinput = key.nextLine();
deposit = Integer.parseInt(userinput);
}
catch (Exception e){
if (!userinput.equals("exit")){
System.out.println("Didn't recognize that input, please try again...");
}
else{
break;
}
}
} while (!userinput.equals("exit"));
annually += deposit * Math.pow((1 + rate/1),year);
monthly += deposit * Math.pow((1 + rate/12),year);
daily += deposit * Math.pow((1 + rate/365),year);
System.out.println(annually);
System.out.println(monthly);
System.out.println(daily);
}
}
Depending on how you want the output, you can easily adjust the scope of the loop to display the amounts after each valid deposit input, or just once at the end, after the user enters "exit".
Hope this helps.

IF ELSE Statement way

I made a program to calculate total price based on user's input. It is working fine, but i would like to know how to cut the code but to have the same output.
Especially on IF ELSE statement, I would like to know how not to repeat myself in those blocks. Is there any other way I can write ouputs after IF ELSE blocks, or they have to be individually inside of those blocks? Thanks.
Here is the code
import java.util.Scanner;
import java.text.*;
public class GasCalc
{
public static void main(String[] args)`enter code here`
{
double gasPrice,carGallons,fullTank,totalPrice;
Scanner input=new Scanner(System.in);
System.out.print("Do you want to calculate full tank (y/n) ");
String askMe=input.next();
if
(askMe.equalsIgnoreCase("y"))
{
DecimalFormat num=new DecimalFormat("$,###.00");
System.out.print("What is the price of 1 gallon of gas ? ");
gasPrice=input.nextDouble();
System.out.print("How many gallons does your vehicle accept ? ");
fullTank=input.nextDouble();
totalPrice=gasPrice*fullTank;
System.out.println("You will pay "+num.format(totalPrice)+" for the full tank of gas");
}
else
if(askMe.equalsIgnoreCase("n"))
{
DecimalFormat num=new DecimalFormat("$,###.00");
System.out.print("How many gallons do you need ? ");
carGallons=input.nextDouble();
System.out.print("What is the price of 1 gallon of gas ? ");
gasPrice=input.nextDouble();
totalPrice=gasPrice*carGallons;
System.out.println("You will pay "+num.format(totalPrice)+" for "+carGallons+" gallons of gas");
}
}
}

If I understand your question correctly - you don't want to repeat the same code in the 'if' and the 'else' parts of an if statement.
The way you would do this is to the same as anywhere else: extract the common code as a function/method which is called from both places.

You can move the last two statements outside, that way your calculation and printing can be done outside the if-else block.
You can rename fullTank and carGallons to gallons, so both variables have the same name, that way the last two statements can be used outside if-else.
totalPrice=gasPrice*gallons;
System.out.println("You will pay "+num.format(totalPrice)+" for the full tank of gas");

Use a method and factorize the local variable num, used in both if and else :
public class GasCalc {
private static double readDouble(Scanner in, String msg) {
System.out.print(msg);
return in.nextDouble();
}
private static String readString(Scanner in, String msg) {
System.out.print(msg);
return in.next();
}
public static void main(String[] args) {
double gasPrice, carGallons, fullTank, totalPrice;
Scanner input = new Scanner(System.in);
String askMe = readString(input,"Do you want to calculate full tank (y/n) ");
DecimalFormat num = new DecimalFormat("$,###.00");
if (askMe.equalsIgnoreCase("y")) {
gasPrice = readDouble(input,"What is the price of 1 gallon of gas ? ");
fullTank = readDouble(input,"How many gallons does your vehicle accept ? ");
totalPrice = gasPrice * fullTank;
System.out.println("You will pay " + num.format(totalPrice) + " for the full tank of gas");
} else if (askMe.equalsIgnoreCase("n")) {
carGallons = readDouble(input,"How many gallons do you need ? ");
gasPrice = readDouble(input,"What is the price of 1 gallon of gas ? ");
totalPrice = gasPrice * carGallons;
System.out.println("You will pay " + num.format(totalPrice) + " for " + carGallons + " gallons of gas");
}
}
}
You could actually factorize even more but it would make little sense to create another method for such a specific treatment. If you are using JDK 8 and understand the lambda expressions, go for it.

How do I make my program continue only if the user enters certain values?

My code is supposed to simulate something similar to a vending machine. But there is a problem when I enter a price that is not one of my options, e.g. 0.82 the program still runs. How do I get it to only accept one of my options?
import java.util.Scanner;
public class VendingMachine
{
public static void main (String[] args)
{
double price;
Scanner keyboard = new Scanner(System.in);
System.out.println("Choose your price. Your options are: ");
double i;
for (i=0.25; i<=1.25; i+=0.25)
System.out.printf("$%.2f\n", i );
System.out.println("Enter your selection now: ");
price=keyboard.nextDouble();
System.out.printf("You chose the $%.2f option. ",price);
double deposit;
if (price<=1.00) {
System.out.println("Please insert 1 dollar. *This machine only accepts Loonies*");
deposit=1;
} else {
System.out.println("Please insert 2 dollars.*This machine only accepts Loonies*");
deposit=2;
}
System.out.println("Please press 'Enter' to simulate inserting money. ");
new Scanner(System.in).nextLine();
double change;
change = deposit-price;
System.out.printf("Your change is $%.2f\n",change);
}
}
I tried something like this but it doesn't work. What is the best way to do this.
if (price==i)
System.out.println("You entered " + price);
else {
System.out.println("Invalide choice. Please try again.")
System.exit(0);
}
Here is an image if you find it easier to read.

You can use some sort of loop (while, do-while, for), which will continue to excecute the code until a condition is (or isn't) met.
Here is an example:
do {
code line 1;
code line 2;
code line 3;
...
} while(yourCondition);
If yourCondition is satisfied (yourCondition == true), the code will go back to code line 1 (will perform the code block between do and while) and it'll stop once the condition isn't satisfied(yourCondition == false). yourCondition could be any expression that returns a true/false result (boolean), such as 2+2==4.
If you want to keep looping for as long as yourCondition isn't met, you can add a ! before your expression, which will evaluate the opposite of your boolean like this (!yourCondition).
Now, if you understood how that works, you can easily apply it to your code.

If you want the user to enter only your displayed prices, I suggest the following, you shall edit to your exact desires.
//given you an open scanner
boolean isCorrectPrice = false;
System.out.println("enter price");
price = in.nextDouble();
while(!isCorrectPrice)
{
if(price%0.25==0 && price<=1.25 && price>0)
{
System.out.println("you entered "+price);
IsCorrectPrice = true;
continue;
}
System.out.println("incorrect price, re-enter ");
price = in.nextDouble();
}
//your code after user enters correct price
That will do the check. If your prices change, all you have to do is change the maximum price provided its still dividable with 0.25 or the condition price check.

Use BigDecimal (instead of double) to work with money. Its exact -- double isn't.
http://docs.oracle.com/javase/6/docs/api/java/math/BigDecimal.html
I would write a function to get the user input. It would not return until the
user had entered an allowed value.

Although my real answer is the one on the comments, you can use something like this. To check recursively if the correct value was given.
import java.util.Scanner;
public class VendingMachine {
static Scanner keyboard = new Scanner(System.in);
public static void main(String[] args) {
System.out.println("Choose your price. Your options are: ");
for (double i = 0.25; i <= 1.25; i += 0.25) {
System.out.printf("$%.2f\n", i);
}
double price = checkMultipleValues(0.25,1.25, 0.25);
System.out.printf("You chose the $%.2f option. ", price);
double deposit;
if (price <= 1.00) {
System.out.println("Please insert 1 dollar. *This machine only accepts Loonies*");
deposit = 1;
} else {
System.out.println("Please insert 2 dollars.*This machine only accepts Loonies*");
deposit = 2;
}
System.out.println("Please press 'Enter' to simulate inserting money. ");
new Scanner(System.in).nextLine();
double change;
change = deposit - price;
System.out.printf("Your change is $%.2f\n", change);
}
private static double checkMultipleValues(double initial,double last,double step) {
System.out.println("Enter your selection now: ");
double price = keyboard.nextDouble();
for (double i = initial; i <= last; i += step) {
if (price == i) {
return price;
}
}
return checkMultipleValues( initial, last, step);
}
}
ADDENDUM
Since you like #Sello answer why don't you combine it with #MrD and have something like
do {
System.out.println("enter price");
price = in.nextDouble();
// System.out.println("you entered " + price);
} while (!(price % 0.25 == 0 && price <= 1.25 && price > 0));

monthly payment calculator

I have some code which I find to keep giving me a dividing by 0 error.
It is suppose to calculate the monthly payment amount!
import java.io.*;
public class Bert
{
public static void main(String[] args)throws IOException
{
//Declaring Variables
int price, downpayment, tradeIn, months,loanAmt, interest;
double annualInterest, payment;
String custName, inputPrice,inputDownPayment,inputTradeIn,inputMonths, inputAnnualInterest;
BufferedReader dataIn = new BufferedReader(new InputStreamReader(System.in));
//Get Input from User
System.out.println("What is your name? ");
custName = dataIn.readLine();
System.out.print("What is the price of the car? ");
inputPrice = dataIn.readLine();
System.out.print("What is the downpayment? ");
inputDownPayment = dataIn.readLine();
System.out.print("What is the trade-in value? ");
inputTradeIn = dataIn.readLine();
System.out.print("For how many months is the loan? ");
inputMonths = dataIn.readLine();
System.out.print("What is the decimal interest rate? ");
inputAnnualInterest = dataIn.readLine();
//Conversions
price = Integer.parseInt(inputPrice);
downpayment = Integer.parseInt(inputDownPayment);
tradeIn = Integer.parseInt(inputTradeIn);
months = Integer.parseInt(inputMonths);
annualInterest = Double.parseDouble(inputAnnualInterest);
interest =(int)annualInterest/12;
loanAmt = price-downpayment-tradeIn;
//payment = loanAmt*interest/a-(1+interest)
payment=(loanAmt/((1/interest)-(1/(interest*Math.pow(1+interest,-months)))));
//Output
System.out.print("The monthly payment for " + custName + " is $");
System.out.println(payment);
// figures out monthly payment amount!!!
}
}
the problem occurs when attempting to set the payment variable.
i don't understand why it keeps coming up with dividing by 0 error.

You have declared your variables as Int so 1/interest and 1/(interest*Math.pow(1+interest,-months)) will return 0. Change the type of your variables to float or double.

One suggestion to you, is that you should learn to "backwards slice" your code.
This means that when you see that you're getting a DivideByZeroException you should look at your code, and say, "why could this happen?"
In your case, let's look at this:
payment=(loanAmt/((1/interest)-(1/(interest*Math.pow(1+interest,-months)))));
So, now, Math.pow will never return anything zero (as it's a power), so it must be the case that interestis zero. Let's find out why:
interest =(int)annualInterest/12;
So now, integer division in Java truncates. This means that if you have .5 it will be cut off, and turned into zero. (Similarly, 1.3 will be truncated to 0).
So now:
annualInterest = Double.parseDouble(inputAnnualInterest);
This implies that you are passing in something that gets parsed to a value that is less than 12. If it were greater than 12 then you would get something else.
However, you might just be passing in an invalid string, for example, passing in "hello2.0" won't work!

This will be rounding always to 0. So it is trowing exception.
(1/interest)-(1/(interest*Math.pow(1+interest,-months)))));
Use float type instead of int. Learn how they works.

package computeloan;
import java.util.Scanner;
public class ComputeLoan {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print(" Enter Yearly Interest Rate : ");
double annualIntersetRate = input.nextDouble();
double monthlyIntersetRate = annualIntersetRate / 1200;
System.out.print(" Enter Number of years : ");
int numberOfYears = input.nextInt();
// Enter loan amount
System.out.print(" Enter Loan Amount : ");
double loanAmount = input.nextDouble();
double monthlyPayment = loanAmount * monthlyIntersetRate /(1-1/Math.pow(1+monthlyIntersetRate,numberOfYears*12 ));
double totalPayment = monthlyPayment * numberOfYears * 12;
//Calculate monthlyPaymeent and totalPayment
System.out.println(" The Monthly Payment Is : " +(int)(monthlyPayment*100) /100.0);
System.out.println(" The Total Payment Is : " +(int)(totalPayment*100) /100.0 );
}
}

Java loan calculator

I'm trying to code a loan calculator. I seem to be having issues. I am trying to get an input from the user and validate the input. I know I am doing it wrong the problem is I'm scratching my head wondering how to do it right.
I get a red line on the d = getDouble(sc, prompt); and the i = getInt(sc, prompt); which I understand I don't have that coded correctly. I'm just unsure how to go about fixing it.
I also have to validate the continue statement which I wasn't to sure the best way to go about that and finally the instructor expects the code to be 80 lines or less which I am right about 80 lines. I guess I'm looking for a better way to do this but being new I'm scratching my head and I'm hoping someone can lend a hand.
As always I really appreciate the help.
import java.util.Scanner;
import java.text.NumberFormat;
public class LoanCalculator
{
public static double getDoubleWithinRange(Scanner sc, String prompt, double min, double max)
{
double d = 0.0;
boolean isValid = false;
while(isValid == false);
{
d = getDouble(sc, prompt);
if (d <= min)
{
System.out.println("Error! Number must be greater tha 0.0");
}
else if (d >= max)
{
System.out.println("Error number must be less than 1000000.0");
}
else
isValid = true;
}
return d;
}
public static int getIntWithinRange(Scanner sc, String prompt, int min, int max)
{
int i = 0;
boolean isvalid = false;
while(isvalid == false)
{
i = getInt(sc, prompt);
if (i <= min)
System.out.println("Error! Number must be more than 0");
else if (i >= max)
System.out.println("Error! Number must be less than 100");
else
isvalid = true;
}
}
public static void main(String[] args)
{
System.out.println("Welcome to the loan calculator");
Scanner sc = new Scanner(System.in);
String choice = "y";
while (choice.equalsIgnoreCase("y"))
{
System.out.println("DATA ENTRY");
double loanAmount = getDoubleWithinRange(sc, "Enter loan amount: ", 0.0, 1000000.0);
double interestRate = getDoubleWithinRange(sc, "Enter yearly interest rate: ", 0, 20);
int years = getIntWithinRange(sc, "Enter number of years: ", 0, 100);
int months = years * 12;
double monthlyPayment = loanAmount * interestRate/
(1 - 1/Math.pow(1 + interestRate, months));
NumberFormat currency = NumberFormat.getCurrencyInstance();
NumberFormat percent = NumberFormat.getPercentInstance();
percent.setMaximumFractionDigits(3);
System.out.println("RESULST");
System.out.println("Loan Amount" + currency.format(loanAmount));
System.out.println("Yearly interest rate: " + percent.format(interestRate));
System.out.println("Number of years: " + years);
System.out.println("Monthly payment: " + currency.format(monthlyPayment));
System.out.println();
System.out.println("Continue? (y/n): ");
choice =sc.next();
System.out.println();
}
}
}

You haven't made the implementation of your getDouble(Scanner,String) and getInt(Scanner,String) that's why you're getting the red line.
since you already have a scanner, and prompt string change it to this
System.out.print(prompt);
d = sc.nextDouble();
and for the integer
System.out.print(prompt);
i = sc.nextInt();

I think getDouble and getInt are string functions so you would have to get a string first then call those methods. However, since you have a scanner, I assume you want to use that with the nextXXX methods:
Scanner sc = new Scanner (System.in);
double d = sc.nextDouble();
You can use this complete snippet for educational purposes:
import java.util.Scanner;
class Test {
public static void main (String args[]) {
Scanner sc = new Scanner (System.in);
System.out.print("Enter your double: ");
double d = sc.nextDouble();
System.out.print("Enter your integer: ");
int i = sc.nextInt();
System.out.println("You entered: " + d + " and " + i);
}
}
Transcript:
Enter your double: 3.14159
Enter your integer: 42
You entered: 3.14159 and 42
Basically, the process is:
Instantiate a scanner, using the standard input stream.
Use print for your prompts.
Use the scanner nextXXX methods for getting the input values.
A little more assistance here, based on your comments.
In your main function, you have:
double loanAmount = getDoubleWithinRange(sc, "Enter loan amount: ", 0.0, 1000000.0)
and that function has the prototype:
public static double getDoubleWithinRange(
Scanner sc, String prompt, double min, double max)
That means those variables in the prototype will be set to the values from the call. So, to prompt for the information, you could use something like (and this is to replace the d = getDouble(sc, prompt); line):
System.out.print(prompt);
double d = sc.nextDouble();
And there you have it, you've prompted the user and input the double from them. The first line prints out the prompt, the second uses the scanner to get the input from the user.
As an aside, your checks for the minimum and maximum are good but your error messages have hard-coded values of 0 and 100K. I would suggest that you use the parameters to tailor these messages, such as changing:
System.out.println("Error! Number must be greater tha 0.0");
into:
System.out.println("Error! Number must be greater than " + min);
That way, if min or max change in future , your users won't get confused :-)
I'll leave it up to you to do a similar thing for the integer input. It is your homework, after all :-)