正确的用户输入不匹配数组值

Question

I've written a portion of code to take a user input, match it to a string value and then use a related double value to make calculations:

double [] currency = new double[] {0.05,0.10,0.20,0.50,1.00,2.00,5.00,10.00,20.00,50.00,100.00};
String [] currencytext = {"$0.05","$0.10","$0.20","$0.50","$1.00","$2.00","$5.00","$10.00","$20.00","$50.00","$100.00"};
Scanner keyboard = new Scanner(System.in);

for (int i = 0; i < currencytext.length; i++) {
    boolean valid = false;
    while(!valid){
        System.out.format("$%.2f remains to be paid. Enter coin or note: ",sum);
        String payment = keyboard.next();
        if(payment.equals(currencytext[i])){
            sum = sum - currency[i];
            if(sum == 0) {
                System.out.print("You gave " + payment);
                System.out.print("Perfect! No change given.");
                System.out.print("");
                System.out.print("Thank you" + name + ".");
                System.out.print("See you next time.");
                }
                }
        if(!(payment.equals(currencytext[i]))) {
            System.out.print("Invalid coin or note. Try again. \n");
                }
        if(payment.equals(currencytext[i]) && currency[i] > sum){
            System.out.print("You gave " + payment);
            System.out.print("Your change:");
        }
    }
}   

The problem is that when it gets to user input, it doesn't match any string values except for $0.05. It seems to me like its not iterating through the array properly but I can't figure out why. Is anyone able to see a problem here?

Answer 1

Too many flaws to point out.

However,

When the currencytext[i] does not match payment , it executes this code:

System.out.print("Invalid coin or note. Try again. \n");
System.out.format("$%.2f remains to be paid. Enter coin or note: ",sum);
payment = keyboard.next();

So, it executes this for all the times that your input does not match currencytext[i] . And, in this block, you have

payment = keyboard.next();

So, it asks for new input, in this block itself. Hence, you get the said output for all inputs except $0.05 .

As far as $0.05 is concerned, your first if block executes successfully, and prints no output. So, it moves to the next iteration of the while loop, where again, payment remains the same ( $0.05 ), but currencytext[i] becomes $0.10 . SO they do not match, and you get the said output.

How to correct this:

With this code, you need to do a lot of corrections.

I suggest you again start from scratch.

Answer 2

If it doesn't fit, it sets valid to true, so the code just has the chance to check against the first item at currencytext[0] , which is $0.05 . Then !payment.equals(currencytext[i]) is also true, and your code prints the lines there. Your else if s are also not properly nested.

Answer 3

This is a possible solution for your problem

    Scanner keyboard = new Scanner(System.in);

    double [] currency = new double[] {0.05,0.10,0.20,0.50,1.00,2.00,5.00,10.00,20.00,50.00,100.00};
    String [] currencytext = {"$0.05","$0.10","$0.20","$0.50","$1.00","$2.00","$5.00","$10.00","$20.00","$50.00","$100.00"};

    String payment = keyboard.next();

    double sum = 100; // <- Working example - Read sum from keyboard entry

    while (sum > 0) {

        boolean paymentFound = false;

        for (int i = 0; i < currencytext.length; i++) {

            if (payment.equals(currencytext[i])) {

                sum = sum - currency[i];
                paymentFound = true;

                if (sum == 0) {
                    System.out.println("You gave " + payment);
                    System.out.println("Perfect! No change given.");

                    // System.out.print("Thank you" + name + ".");

                    System.out.println("See you next time.");
                    break;
                } else if (sum < 0) {
                    System.out.println("You gave " + payment);
                    System.out.println("Your change:" + (-1 * sum));
                    break;
                }
            }
        }

        if (!paymentFound) {
           System.out.println("Invalid coin or note. Try again. \n");

        }

        if (sum > 0) {
            System.out.format("$%.2f remains to be paid. Enter coin or note: ", sum);
            payment = keyboard.next();
        }
    }

while-loop will continue until the payment is fullfilled.

for-loop traverse the arrays until a suitable payment is found

• If suitable payment is found we substract it from sum . We use break to exit the for-loop in both cases. There is no need to keep searching.

• If no suitable payment is found [ !paymentFound ], we keep on asking.

    if (!paymentFound) { System.out.println("Invalid coin or note. Try again. \\n"); } if (sum > 0) { System.out.format("$%.2f remains to be paid. Enter coin or note: ", sum); payment = keyboard.next(); } 

The program will end when (sum < 0), in which case the while-loop exits. I have use println instead of print to improve message legibility.

Answer 4

I don't know how you are reading input. One improvement you can do is write reading input code in for loop.

Scanner scanner = new Scanner(System.in);
for (... ) {
....
String payment = scanner.nextLine();
....
}