How Can I Get This While Loop to Run When Using a Sentinel Value for a Variable with Scanner Input Inside of the Loop, While Calling Methods?
2 Months into My First Java Programming. I'm Trying to Create a While Loop in a Class with Methods and Scanner Inputs. Attempting to Use a Sentinel Value to...
2 months into my first java programming. I'm trying to create a while loop in a class with methods and scanner inputs. Attempting to use a sentinel value to break out of the while loop. I've attempted while loops, do-while loops, with and without if-else blocks.
It looks like it's requiring me to initialize the salePrice for it to work, but the salePrice is entered by the user inside the loop. I have tried to assigning a fake value to it before the while loop, it then lets me start the loop, but 0 does not break of out of it, it just goes to the second question in the loop.
Is there something fundamentally wrong with this logic structure? Do the methods create a different need? I'm only 2 months into coding, so it has to be a very simple answer... Do I need to put if-else logic within the while loop just to break out of the loop with a sentinel value in this case?
public class PurchaseCalculator {
//create main method
public static void main(String[] args) {
// declare variables
// double salePrice;
double discount = .15;
double maxPurchaseAmount;
double salePrice;
// create scanner object
Scanner userInput = new Scanner(System.in);
while (salePrice > 0){
// prompt user to enter price
System.out.println("Enter the price of the item. Enter 0 to end program");
// read in price from user and store in sale price
salePrice = userInput.nextDouble();
//create a scanner object for salesPrice input
System.out.println("Price entered: $" + salePrice);
//prompt user to enter max purchase amount
System.out.println("Enter the maximum purchase amount");
// read in max amount from user and store in maxPurchaseAmount
maxPurchaseAmount = userInput.nextDouble();
// call displaypricewithtax method
displayPriceWithTax(salePrice);
// call computePriceAfterDiscountMethod
computePriceAfterDiscount(salePrice, discount);
// call displaypurchasablelimit method
displayPurchasableNumber(salePrice, maxPurchaseAmount);
} // close while loop
} //close main
1 Answer
In Java any local variable1 must be initialized before its value can be read. Not to be confused with class fields2, which are initialized with default values.
1 - variables declared inside statement blocks ({...})
2 - instance variables or class variables
Option 1: change the while loop to a do-while loop. Using this, the check is done after the iteration, so a value is assigned to the variable:
double salePrice;
do {
...
salePrice = userInput.nextDouble();
...
while (salePrice > 10);
To avoid execution of the rest of the iteration, an if can be used; but mostly the next option (Option 2) is used instead:
double salePrice;
do {
...
salePrice = userInput.nextDouble();
if (salePrice >0) {
...
}
while (salePrice > 10);
Option 2: use an if inside the loop:
while (true) { // for ever
...
salePrice = userInput.nextDouble();
if (salePrice <= 0)
break;
}
Option 3: use a flag (boolean) to control the loop
boolean stop = false;
while (!stop) {
...
salePrice = userInput.nextDouble();
stop = salePrice <=0;
...
}
Option 4: assign a fake initial value:
double salePrice = 1.0;
while (salePrice > 0) {
...
salePrice = userInput.nextDouble();
...
}
(I would suggest going by first or second option, eventually 3rd for some cases)
Sarah Jenkins is a veteran tech journalist with over 12 years of experience covering artificial intelligence, mobile innovations, and digital ethics. Her insights have appeared in leading technology publications worldwide.
