java - 正确的用户输入与数组值不匹配

Question

我编写了一部分代码来获取用户输入，将其与字符串值匹配，然后使用相关的 double 值进行计算:

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:");
        }
    }
}   

问题是，当它获取用户输入时，它不匹配除 $0.05 之外的任何字符串值。在我看来，它没有正确遍历数组，但我不明白为什么。有人能看出这里有问题吗？

Answer 1

这是您问题的可能解决方案

    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 将继续执行，直到付款完成。

for循环遍历数组，直到找到合适的付款

• 如果找到合适的付款，我们会从总和中减去它。在这两种情况下，我们都使用 break 退出 for 循环。没有必要继续寻找。

• 如果找不到合适的付款 [! paymentFound]，我们将继续询问。

      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();
      }
  

程序将在 (sum < 0) 时结束，在这种情况下 while 循环退出。我使用 println 而不是 print 来提高消息的易读性。