Develop Reference

How do I convert my while loop to a for loop?

I am a beginner coder using Netbeans Java. I have created a code that initially asks how many gallons are in your gas tank. Then, it will have a while loop asking how many miles you will be traveling for this first run and how fast are you traveling. This will repeat with a while loop until you input '0' to stop adding trips. I am stumped on how to convert this while loop into only using For loops. I would greatly appreciate the assistance. Here is my code that has while loops.
public static void main(String[] args)
{
Scanner input = new Scanner(System.in);
int tank;
double miles;
double speed;
double totalMiles = 0.0;
int choice;
double time;
double totalTime = 0.0;
double fuelConsumption;
System.out.print("How many gallons of gas is in your tank (Integer 1-15)? ");
tank = input.nextInt();
System.out.printf("%s%d%s\n\n" , "You have ", tank , " gallons of gas in your tank.");
System.out.print("Are you going on a trip (1 = Yes or 0 = No)? ");
choice = input.nextInt();
while (choice == 1)
{
System.out.print("How many miles are you traveling? "); // miles
miles = input.nextFloat();
System.out.print("What is your speed for this run (MPH)? "); // speed
speed = input.nextInt();
System.out.print("\n");
totalMiles = totalMiles + miles;
time = (miles/speed);
totalTime += (time*60);
fuelConsumption = (20*(tank/totalMiles));
System.out.print("Is there another leg in your trip (1 = Yes or 0 = No)? "); // asking another leg
choice = input.nextInt();
if (choice == 0)
{
System.out.printf("%s%5.2f%s\n","Your data for this trip is: \n"
+ "You traveled a total of about ", totalMiles , " miles.");
System.out.printf("%s%.2f%s\n" , "You traveled about " , totalTime , " minutes.");
if (fuelConsumption >= 2)
{
System.out.println("Your car has enough gas to return.");
break;
}
else
{
System.out.println("Your car will need more gas to return.");
break;
}
}
}
}
}

That is not a use case for a for loop, where we iterate over a known number of elements for do a known number of iterations. Like, repeat 10 times or such.
Technically it can be solved with a for loop, but that is abusing the concept a bit. The while loop is a perfect fit for that task.

This is not a place to use a for-loop, you use a for loop for something like this:
printAmount = 10;
for (int i = 0; i < printAmount; i++) {
System.out.println("Hello World");
}
Here you are using the for loop to print "Hi" for the amount in printAmount.
Your case is different: You want the while-loop to repeat while the input is "1" so you use a WHILE-loop.

Display bill total, Java public void display() error

I'm having some trouble executing the total bill display. I asked my professor who gave me this small block of code, which I modified to meet my needs, but for some reason it is not executing and has the error:
Illegal start to expression for line --> public void display().
The compiler also suggests to end with a semi colon which I don't believe is accurate.
What am I missing that public void display() is not being executed and is erroneous?
import java.util.Scanner;
public class CoffeeShop
{
/* Author:
Date:
Program: Create a Coffee Shop application that uses a while loop to build a customer order. The Coffee Shops sells coffee ($3.25), espresso ($4.25), and tea ($2.75). The coffee selection presents the customer with the choices of iced (no charge), cream (50 cents), and sugar (50 cents). The espresso selection presents the customer with choice of caramel (no charge) and chocolate (no charge) with one shot (no charge) or two shots ($1.25) of espresso. Once the customer is done, he or she will receive a bill of the total price. After each selection, the customer will have the choice of returning to the main menu for additional purchases. Use nested loops to handle customers' submenu selections.
*/
public static void main(String[] args)
{
//declarations
double coff = 3.25;
double esp = 4.25;
double tea = 2.75;
double cream = .50;
double sugar = .50;
double dblShot = 1.25;
int dblshotQty = 0;
int userInput = 0;
int userInput2 = 0;
int coffQty = 0;
int espQty = 0;
int teaQty = 0;
int creamQty = 0;
int sugarQty = 0;
double runTotal = 0;
double totalCoff = 0;
double totalEsp = 0;
double totalTea = 0;
double totalBill = 0;
Scanner scan = new Scanner(System.in);
System.out.print("Would you like to place an order? press 1 for yes or 2 for no :");
//start a loop with a control variable asking if they would like a cup of coffee yes or no
userInput = scan.nextInt();
while(userInput == 1)
{
System.out.print("Enter 1 for Coffee, 2 for Espresso, or 3 for tea: ");
userInput2 = scan.nextInt();
switch(userInput2)
//if 1 is pressed coffee is ordered
{ // open switch
case '1':
{
coffQty = coffQty + 1;
System.out.print("Press 1 if you would like your coffee iced or 2 for no: ");
userInput = scan.nextInt();
}
{
System.out.print("Press 1 if you would like cream for $.50 or 2 for no: ");
userInput = scan.nextInt();
if ( userInput == 1 )
{
creamQty = creamQty + 1;
}
}
{
System.out.print("Press 1 if you would like sugar for $.50 or 2 for no: ");
userInput = scan.nextInt();
if ( userInput == 1 )
{
sugarQty = sugarQty + 1;
}
}//end case 1
break;
// espresso is ordered ask for double shot
case '2':
{
espQty = espQty +1;
System.out.println("Press 1 for a double shot for $1.25 or 2 for no: ");
userInput = scan.nextInt();
if(userInput == 1)
{
dblshotQty = dblshotQty +1;
}
}//end case 2
break;
//tea is ordered
case '3':
{
teaQty = teaQty + 1;
System.out.println("You have selected tea! Great Choice.");
}//end case 3
}//end switch
// create output display for total bill adding all totals
public void display()
{
double totalCoff = coffQty * coff + cream * creamQty + sugar * sugarQty;
double totalEsp = espQty * esp + dblshot * dblshotQty;
double totalTea = teaQty * tea;
System.out.println("Order: \n "+coffQty + " Coffee"
+ "\n "+creamQty +" Cream"
+ "\n "+sugarQty + " Sugar"
+ "\nTotal Coffee: "+ totalCoff);
System.out.println(" "+teaQty + " Tea"
+ "\nTotal Tea: "+ totalTea);
System.out.println(" "+espQty + " Espresso"
+ "\n "+dblshotQty +" Double shot"
+ "\nTotal Espresso: "+ totalEsp);
double totalBill = totalCoff+totalEsp+totalTea;
System.out.println("\nTotal drink order: "+totalBill);
}
break;
} // end while
}
} // end of class

Your code structure is making things difficult for you. As mentioned by #Carcigenicate, (nice name btw), you have you declared a method inside the main method. Once you change that, you'll notice now that now the display method shows compiler errors. This is because the variables referenced in display are no longer visible. You have a few options:
Rethink the design of the class i.e What methods should exist and how they will be called.
Take the display method outside the main method and then make the variables member variables that are visible to the methods you need. Read about the effects of using member variables first.
Remove the display method completely and move the logic to the main method.

I see a few main problems:
You defined display inside of main, inside of a while loop. You can't define methods inside of methods, let alone inside of loops. Move display outside of main, but still inside the class.
You have a misplaced break floating around under display. Get rid of that, as that will also be an error.
As #MiiinimalLogic pointed out, you're relying on data from main inside of display. You'll need to pass the data from main to display as arguments.

Writing for loops/while loops?

I'm in a programming class in high-school, and I was given an assignment to make a basic subtotal and top calculator, but I work at a restaurant, so it seemed a little pointless to make a calculator that only let you read in one food. So I tried to make it able to take in multiple food items and add them to one price variable. Sorry if some of this code may seem inefficient or redundant. It's only high-school of course.
The issue is, when I run it, it gets up to the asking if there was another food item the user would like to add, and when I type in "Yes" or "No", the program does nothing. Keeps running, but goes no further. Any explanations?
import java.text.NumberFormat;
import java.util.Scanner;
public class Price {
/**
* #param args
*/
public static void main(String[] args) {
final double taxRate = .0887; //8.87% Tax Rate
double tipRate;
int quantity1;
Scanner kb = new Scanner(System.in);
double subtotal, tax, tip, totalCost1, unitPrice1 = 0;
String done;
System.out.println ("How many of the first item did you get?: ");
quantity1 = kb.nextInt();
for (int i = 0; i < quantity1; i++)
{
System.out.println ("What was the price of that single item "+(i+1) + ": ");
unitPrice1 = kb.nextDouble();
System.out.println ("Was there another food item you'd like to add?: ");
done=kb.next();
while (done.equalsIgnoreCase("Yes"));
}
System.out.println ("What percent would you like to tip? (Formatted like 0.10 for 10%, 0.20 for 20%, etc.): ");
tipRate = kb.nextDouble();
subtotal= quantity1 * unitPrice1;
tax = subtotal * taxRate;
totalCost1 = subtotal + tax;
tip = totalCost1 * tipRate;
totalCost1 = totalCost1 + tip;
//Formatting
NumberFormat money = NumberFormat.getCurrencyInstance();
NumberFormat tipMoney = NumberFormat.getCurrencyInstance();
NumberFormat taxPercent = NumberFormat.getPercentInstance();
NumberFormat tipPercent = NumberFormat.getPercentInstance();
System.out.println ("Your total before tax is: " + money.format(subtotal));
System.out.println ("The tax is " + money.format(tax) + " at " + tipPercent.format(taxRate));
System.out.println ("The tip at " + tipPercent.format(tipRate) + " is " + tipMoney.format(tip));
}
}

You have an infinite loop here:
while (done.equalsIgnoreCase("Yes"));
Once you enter Yes, it will keep sitting there and doing nothing because the value of done is Yes and never changes.
Also your loop structure is a bit odd. Your outer for loop runs as many times as the quantity of the first item. But shouldn't you only be multiplying that number to the cost? Because you are either running the loop for as long as the number of items the user entered (by asking them up front) or you don't ask them the total number of items and simply ask them to enter Yes if they want to add more items; you can't really do both.
Your loop should probably look something like this:
String input = "Yes";
while(input.equalsIgnoreCase("Yes")) {
System.out.println ("How many of the first item did you get? ");
quantity1 = kb.nextInt();
System.out.println ("What was the price of that single item? ");
unitPrice1 = kb.nextDouble();
//total += unitPrice1 * quantity1 - you don't have this in your code, but this is where you would be calculating the running total
System.out.println("Was there another food item you'd like to add? ");
input = kb.next();
}

you need to exit for loop when user enters yes, so you can use label here like below:
outerloop:
for (int i = 0; i < quantity1; i++)
{
System.out.println ("What was the price of that single item "+(i+1) + ": ");
unitPrice1 = kb.nextDouble();
System.out.println ("Was there another food item you'd like to add?: ");
done=kb.next();
while (done.equalsIgnoreCase("Yes")){
break outerloop;
}
}
Your current code does not do anything inside the while loop if you don't enter yes. And if you enter yes it will be stuck in infinite loop because of your while loop. This is not the efficeint way of looping, but this code will have least change in your current code.

You're while loop is doing nothing, you had given it a condition, but it has no instruction.
Try something like this..(sorry for my rusty java)
'public static void main(String[] args) {
//variable declaration
bool running = true
final double taxRate = .0887; //8.87% Tax Rate
double tipRate;
int quantity1;
Scanner kb = new Scanner(System.in);
double subtotal, tax, tip, totalCost1, unitPrice1 = 0;
String done;
while(running = true){
System.out.println ("How many of the first item did you get?: ");
quantity1 = kb.nextInt();
for (int i = 0; i < quantity1; i++)
{
System.out.println ("What was the price of that single item "+(i+1) + ": ");
unitPrice1 = kb.nextDouble();
System.out.println ("Was there another food item you'd like to add?: ");
done=kb.next();
if(done.equalsIgnoreCase("No")){
running = false
//Allows you to break out of the while loop if the user does not want to add anything else
//DO NOT USE BREAK STATMENTS, IT IS A POOR PROGRAMMING PRACTICE.
};//end if
}//end for
}//end while
System.out.println ("What percent would you like to tip? (Formatted like 0.10 for 10%, 0.20 for 20%, etc.): ");
tipRate = kb.nextDouble();
//You should comment whats going on here
subtotal= quantity1 * unitPrice1;
tax = subtotal * taxRate;
totalCost1 = subtotal + tax;
tip = totalCost1 * tipRate;
totalCost1 = totalCost1 + tip;
//Formatting
NumberFormat money = NumberFormat.getCurrencyInstance();
NumberFormat tipMoney = NumberFormat.getCurrencyInstance();
NumberFormat taxPercent = NumberFormat.getPercentInstance();
NumberFormat tipPercent = NumberFormat.getPercentInstance();
//Output
System.out.println ("Your total before tax is: " + money.format(subtotal));
System.out.println ("The tax is " + money.format(tax) + " at " + tipPercent.format(taxRate));
System.out.println ("The tip at " + tipPercent.format(tipRate) + " is " + tipMoney.format(tip));
}//end main

error in an election program with while loop

I wrote this program to calculate the total number of votes that each person got in an election, and to enter multiple districts. When I try to enter another district the program just prints out the votes received from the first district instead of setting up another poll. What is wrong with it and how do I fix it?
import java.util.Scanner;
public class Election{
public static void main (String[] args){
int votesForPolly = 0; // number of votes for Polly in each precinct
int votesForErnest = 0; // number of votes for Ernest in each precinct
int totalPolly = 0; // running total of votes for Polly
int totalErnest = 0; // running total of votes for Ernest
String response = ""; // answer (y or n) to the "more precincts" question
Scanner scan = new Scanner(System.in);
System.out.println ();
System.out.println ("Election Day Vote Counting Program");
System.out.println ();
// Initializations
// Loop to "process" the votes in each precinct
{
System.out.println ("Enter Votes? Enter Y or N");
response=scan.next().toUpperCase();
if (response.equals("Y")){
response="Yes";
System.out.println ("Enter votes for Polly:");
votesForPolly=scan.nextInt();
totalPolly=totalPolly+ votesForPolly;
System.out.println ("Enter votes for Ernest:");
votesForErnest=scan.nextInt();
totalErnest=totalErnest+ votesForErnest;
System.out.println ("Enter another District? Enter Y or N");
response=scan.next().toUpperCase();
}else{
int count = 0;
while (count == 1){
// Print out the results
}
}
System.out.println ("Total votes for Polly is: " + totalPolly);
System.out.println ("Total votes for Ernest is: " + totalErnest);
}
}
}

Your current looping is broken (because you start with count = 0, therefore while (count == 1) is not entered, I would rewrite it as follows
final String msg = "Enter Votes for District %d?"
+ " Enter Y to continue, N to stop.\n";
// Loop to "process" the votes in each precinct
for (int i = 1;; i++) {
System.out.printf(msg, i);
response = scan.next().toUpperCase();
if (response.startsWith("N")) {
break;
}
System.out.println("Enter votes for Polly: ");
votesForPolly = scan.nextInt();
totalPolly += votesForPolly;
System.out.println("Enter votes for Ernest: ");
votesForErnest = scan.nextInt();
totalErnest += votesForErnest;
}
System.out.printf("Total votes for Polly is: %d\n"
+ totalPolly);
System.out.printf("Total votes for Ernest is: %d\n"
+ totalErnest);

You are not looping through the polling section.
Change
if (response.equals("Y")){
to
while (response.equals("Y")){
and remove the else statement.

Desired output calculation wrong?

I've written this program but am running into a logical error upon compilation.
My input would be 1, 2, 6, 10 for the selection of products and the coinciding output should be
Total items ordered: 3
Price of items ordered: $747.00
Sales Tax: $48.55
Total amount due: $795.55
Strangely enough it is giving me
Total items ordered: 3
Price of items ordered: $6611.00
Sales Tax: $429.715
Total amount due: $7040.715
Is there an error within my for loop conditions or calculations, or my array that is leading to this hyper-inflated output?
import java.util.Scanner;
public class GrapefruitOrderingArray {
//Declare Constants
public static final int SIZE = 100;
public static final int[] itemPrices = {49,299,329,399,199,1299,1199,999,599};
public static void main(String[] args) {
// Declare Variables
Scanner input = new Scanner (System.in);
String CustomerName;
int[] naNumber = new int [SIZE];
int nProducts = 0;
double nTotal = 0;
double dFinalPrice = 0.0;
int nCount = 0;
//Declare Constants
final int SENTINEL = 10;
final double SALES_TAX = 0.065;
//Prompt user to enter name
System.out.println("Please enter your name: ");
//Enter user name
CustomerName = input.nextLine();
System.out.println("");
//Begin Product Listing Declarations with respect to array above
System.out.println("GRAPEFRUIT PRODUCT:");
System.out.println("1. gPod shuffle $" + itemPrices[0]);
System.out.println("2. gPod Touch $" + itemPrices[1]);
System.out.println("3. gPad Mini $" + itemPrices[2]);
System.out.println("4. gPad 2 $" + itemPrices[3]);
System.out.println("5. gPhone $" + itemPrices[4]);
System.out.println("6. gMac $" + itemPrices[5]);
System.out.println("7. MacNovel Pro $" + itemPrices[6]);
System.out.println("8. MacNovel Air $" + itemPrices[7]);
System.out.println("9. MiniMac $" + itemPrices[8]);
System.out.println("10. Complete my order");
//Keep reading until the input is terminated by sentinel
System.out.println("\nPlease select an item from the menu above: ");
//Read number entered by the user
naNumber[nCount] = input.nextInt();
//Begin while-loop statement
while (naNumber[nCount] != SENTINEL) {
System.out.println("\nPlease select another item from the menu above: ");
nCount++;
//Read number entered by the user
naNumber[nCount] = input.nextInt();
}
System.out.println("Thank you for ordering with Grapefruit Company, " + CustomerName);
//Call final price calculation
dFinalPrice = calculateTotalPrice(naNumber,itemPrices,nTotal);
//Print blank line to screen
System.out.println("");
//Total amount of product ordered
System.out.println("Total items ordered: " + nCount );
//Total price of items ordered
System.out.println("Price of items ordered: $" + dFinalPrice );
//Sales tax associated with the purchase
System.out.println("Sales tax: $" + SALES_TAX * dFinalPrice );
//Total amount due by the customer to Grapefruit Co.
System.out.println("Total amount due: $" + (SALES_TAX * dFinalPrice + dFinalPrice ));
} //End main method
private static double calculateTotalPrice(int[] naNumber, int[] itemPrices) {
double total = 0;
//Calculate entered items
for(int i = 0; i < naNumber.length; i++){
if(naNumber[i] != 0) {
total += itemPrices[naNumber[i] - 1];
}
}
return total;
}
} //end class calculateTotalPriceOfItemsOrdered

You naNumber will contain numbers from 1 to 9. This means that you'll be multiplying the item prices by some large numbers at some points, hence why you're getting large totals.
What I think you want to do is
double itemTotal = itemPrices[naNumber[i] - 1];
nTotal += itemTotal;
Without multiplying itemPrices[i] by naNumber[i]
Also you don't really need to pass nTotal to the method and initialise a double with every loop. You can just declare a field outside the loop:
double total = 0;
Use it inside the loop like this:
total += itemPrices[naNumber[i] - 1];
And return it at the end of the method.
So your method would look something like that:
private static double calculateTotalPrice(int[] naNumber, int[] itemPrices) {
double total = 0;
//Calculate entered items
for(int i = 0; i < naNumber.length; i++){
if(naNumber[i] != 0) {
total += itemPrices[naNumber[i] - 1];
}
}
return total;
}

There are three problems here.
You put the sentinel value, 10, into the array of items the user has chosen.
You use the loop index rather than the number the user chose when calculating price.
You multiply the price of each item by its number. So the user buys 6 of item 6.
In your main method, you need to read the user's input into another variable, and only insert it into the array if it is not the sentinel value.
In your calculateTotalPrice method, you should calculate the price of an individual line item like this:
double itemTotal = itemPrices[naNumber[i] - 1];