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.

BMI Calculator. Whats wrong?

I just want to know how to remove that initialized wgt error. Rest, I want my code to be basic and very simple.
//Program By Aryansh Malviya
//BMI Calculator
import java.util.Scanner;
public class BMICalc
{
public static void main(String args[])
{
Scanner input = new Scanner(System.in);
int cw;
int ch;
int bmi;
int wgt;
int hgt;
int ct;
System.out.print("\nNote: This program is not yet fully functional.\nThere might be issues regarding decimal values. \nProgram has not been equipped to accept or display in decimal values. \nThe program will be updated soon. \nSorry for the inconvinience.");
System.out.print("Enter 1 if you want weight in Kilograms");
System.out.print("Enter 2 if you want weight in Pounds");
cw = input.nextInt();
System.out.print("\nNote: If you choose to enter weight in Pounds, you'd have to enter height in Inches. Else, in meters");
if(cw == 1)
{
System.out.print("\nEnter weight in Kilograms: ");
wgt = input.nextInt();
}
else if(cw == 2)
{
System.out.print("\nEnter weight in Pounds: ");
wgt = input.nextInt();
}
else
{
System.out.print("\nEnter a valid choice and try again!");
}
System.out.print("\nEnter your height: ");
hgt = input.nextInt();
bmi = wgt/(hgt * hgt);
System.out.printf("\nYour weight is: %d", wgt);
System.out.printf("\nYour height is: %d", hgt);
System.out.printf("\n\nYour BMI is: %d", bmi);
System.out.print("\nBMI VALUES");
System.out.print("\nUnderweight: less than 18.5");
System.out.print("\nNormal: between 18.5 and 24.9");
System.out.print("\nOverweight: between 25 and 29.9");
System.out.print("\nObese: 30 or greater");
}
}
When I compile the program I get the error that the variable wgt has not been initialized. Please tell me how to solve this problem.

You have two if statements - but if the user enters neither 1 nor 2 you end up in a part of the code where you try to use wgt without ever initializing it.
You should do two things:
First, initialize wgt when you first declare it (that makes the compiler error go away).
int wgt=0;
would do it.
Next, make sure your program traps the case when cw is neither 1 nor 2. You could use a while loop with a flag, or some other mechanism. Right now, a wrong entry for cw will just keep on going (you print "enter a valid choice" but don't actually go back to the beginning…)
Here is how you fix all that:
import java.util.Scanner;
public class BMICalc
{
public static void main(String args[])
{
Scanner input = new Scanner(System.in);
int cw=0;
int ch;
double bmi;
double wgt=0;
double hgt;
int ct;
double BMIinchPoundFactor = 703;
System.out.print("\nNote: This program is not yet fully functional.\nThere might be issues regarding decimal values. \nProgram has not been equipped to accept or display in decimal values. \nThe program will be updated soon. \nSorry for the inconvinience.");
System.out.print("\nNote: If you choose to enter weight in Pounds, you'd have to enter height in Inches. Else, in meters");
boolean validInput = false;
while (!validInput) {
System.out.print("\nEnter 1 if you want weight in Kilograms");
System.out.print("\nEnter 2 if you want weight in Pounds\n");
cw = input.nextInt();
switch(cw) {
case 1:
System.out.print("\nEnter weight in Kilograms: ");
wgt = input.nextDouble();
validInput=true;
break;
case 2:
System.out.print("\nEnter weight in Pounds: ");
wgt = input.nextDouble();
validInput=true;
break;
default:
System.out.print("\nEnter a valid choice and try again!");
}
}
System.out.print("\nEnter your height: ");
hgt = input.nextDouble();
bmi = wgt/(hgt * hgt);
if(cw==2) bmi *= BMIinchPoundFactor;
System.out.printf("\nYour weight is: %.0f", wgt);
System.out.printf("\nYour height is: %.2f", hgt);
System.out.printf("\n\nYour BMI is: %.1f", bmi);
System.out.print("\nBMI VALUES");
System.out.print("\nUnderweight: less than 18.5");
System.out.print("\nNormal: between 18.5 and 24.9");
System.out.print("\nOverweight: between 25 and 29.9");
System.out.print("\nObese: 30 or greater\n\n");
}
}
I took a few other liberties:
Use double for things that might not be integer values
Clean up the I/O (adding some '\n')
Create a loop that keeps going until you give a valid input
Properly compute BMI wen you give an input in pounds and inches
I'm sure it can be further improved…

There is no guarantee that wgt has been initialized. For example, the user could enter '3' to the first question. You should consider and handle illegal inputs.

bmi = wgt/(hgt * hgt);
You are using wgt here and there is possibilities could not initialize if cw is neither 1 nor 2.

Java Tip Calculator for newbie

I hope I'm posting in the right place.
I'm pretty new to Java (meaning this is only my third program besides 'hello world').
I have a tip calculator I'm working on for an assignment. I'm not getting an 'error' as such,
but the method for splitting the bill always seems to think each customer pays 'infinity'.
I have my program set up in two classes: tipCalc1 and tipCalc2 (no points for originality of course).
The program appears to run without issue besides the 'infinity' issue.
Here's what I have so far. Any assistance appreciated, thanks.
***TipCalc1 Class:***
import java.util.Scanner;
public class Tipcalc1
{
public static void main(String[] args)
{
System.out.println("Welcome to Tip Calculator! ");
TipCalc2 Calculator = new TipCalc2();
System.out.println("Please enter the bill amount: ");
TipCalc2.calBill();
System.out.println("What percentage would you like to tip?: ");
Calculator.percTip();
}
}
***And the tipCalc2 class which does the dirty work:***
import java.util.Scanner;
public class TipCalc2
{
static double bill;
double tip;
double total;
double split;
double splitPrompt;
double Y;
double N;
double billPerPerson;
static Scanner scan = new Scanner(System.in);
public static void calBill()
{
bill = scan.nextDouble();
}
public void percTip()
{
tip = scan.nextDouble();
if(tip<1)
{
total = bill * tip;
}
else total = bill * (tip/100);
System.out.println("Your total is: " + total);
Split();
}
public void Split()
{
System.out.println("Would you like to split the bill? ");
System.out.println("Enter 1 for YES or 0 for NO: ");
splitPrompt = scan.nextDouble();
if(splitPrompt == 0)
{
System.out.println("Your total is: " + total);
System.out.println("Thankyou. Goodbye.");
System.out.println("End Program");
}
if(splitPrompt == 1)
{
System.out.println("How many ways would you like to split the bill? ");
splitPrompt = scan.nextDouble();
billPerPerson = total / split;
System.out.println("Each person pays: " + billPerPerson);
System.out.println("Thankyou. Goodbye.");
System.out.println("End Program.");
}
else System.out.println("Invalid Entry");
}
}

The default value for split (because you have not initialized it with another value) is 0.0, therefore, when you do
billPerPerson = total / split;
you divide by 0.0, so you will get Infinity.
Notes:
Since your variable splitPrompt is double and computers doesn't store real values with a 100% accuracy, you shouldn't compare it with 0.0. Since this variable will store 0 or 1 for input, you can declare it as int, which will be accurate.
Try to follow Java naming conventions. Use mixedCase for methods/variables and use CamelCase for classes/interfaces.
In the method split(), you should use an if-else if-else structure:
if(splitPrompt == 0) {
...
}
else if(splitPrompt == 1) {
...
}
else {
...
}

Silly mistake.
Change
System.out.println("How many ways would you like to split the bill?
splitPrompt = scan.nextDouble();
to
System.out.println("How many ways would you like to split the bill?
split = scan.nextDouble();
since you never change split which, like all double variables, is initialized to 0.0.
Also, you should use ints where appropriate as not all of the numbers should be doubles. Or even better, use 'y' and 'n' chars.

Class TipCalc2
//Total = **bill** * (gets percentage in decimal 15 = 0.15) + **bill**
Line 18 needs to be:
total = bill * (tip / 100) + bill;
Line 36/37 needs to be:
split = splitPrompt = scan.nextInt();
billPerPerson = total / split;
//You're dividing billPerPerson = total by ZERO (split);
Line 36/37 original:
billPerPerson = total / split;

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));

I'm trying to find the percentage of calories in fat but my output is never correct

Here's my code
import java.util.Scanner;
import java.text.DecimalFormat;
public class Calories
{
public static void main (String[] args)
{
int fat; //Grams of fat
int fcal; //Calories from fat
int total; //Number of Calories
long result; //Percent of calories from fat
System.out.println("This program finds the percent of calories from fat");
//Here the user inputs the numbers
Scanner keyboard = new Scanner (System.in);
System.out.print("Enter the total grams of fat " );
fat = keyboard.nextInt();
fcal = fat * 9;
System.out.print("Enter the total number of calories " );
total = keyboard.nextInt();
result = fcal / total * 100;
if(result <= 30)
{
System.out.println("Food is low in fat!");
}
DecimalFormat formatter = new DecimalFormat("#0");
System.out.println("Calories from fat : " + formatter.format(result) + "%");
}
}
No matter what I input my output always comes out as zero. Can anyone tell me what I'm doing wrong here? I'm not sure whether DecimalFormat, the datatype, or keyboard.nextInt(); is part of my problem, I've gone over it multiple times and asked another person who said the code was running fine for them.

Your fcal and total variables are both integers, so you're performing integer division. Any time fcal < total, you'll always get 0 as your answer.
You need to cast as a double when doing your division.
That won't quite work either since result is declared as long so there'll be a loss of precision. Either change the datatype of result or else cast the result back to a long.