基本 Java 练习 - 需要帮助

Question

Here are the instructions

Online Book Depot offers premium customers 1 free book with every purchase of 5 or more books and offers 2 free books with every purchase of 8 or more books.

It offers regular customers 1 free book with every purchase of 7 or more books, and offers 2 free books with every purchase of 12 or more books.

Write the block of code that assigns freeBooks the appropriate value based on the values of the boolean variable isPremiumCustomer and the int variable nbooksPurchased

The code compiles without error but results are incorrect:

boolean isPremiumCustomer = false;
    int freeBooks = 0;
    Scanner scanner = new Scanner(System.in);
    System.out.println("Enter the no of books:");
    int nbooksPurchased = scanner.nextInt();
    System.out.println("is Premium customer?(y/n):");
    String ans = scanner.next();
    if (ans.equals("y") || ans.equals("Y") && (nbooksPurchased >4 && (nbooksPurchased <8))) {
        isPremiumCustomer = true;
        freeBooks = 1;
    }else if (ans.equals("y") || ans.equals("Y") && (nbooksPurchased >=8 )) {
        isPremiumCustomer = true;
        freeBooks = 2;
    }else if (ans.equals("n") || ans.equals("N") && (nbooksPurchased >=7 && (nbooksPurchased <=11))) {
        freeBooks = 1;
    }else if (ans.equals("n") || ans.equals("N") && (nbooksPurchased >=12 )){
        freeBooks = 2;
        }
        System.out.println("Free Books:" + freeBooks);

Answer 1

Reading your own code in the comment is hardly possible. When I format it, I get:

if (ans.equals("y") || ans.equals("Y")) {
    isPremiumCustomer = true;
}
if (nbooksPurchased >= 3 && (nbooksPurchased <= 7)) {
    freeBooks = 1;
} else if (nbooksPurchased >= 8) {
    freeBooks = 2;
}
if (ans.equals("n") || ans.equals("N")) {
    if ((nbooksPurchased >= 7 && (nbooksPurchased <= 11))) {
        freeBooks = 1;
    } else if (nbooksPurchased >= 12) {
        freeBooks = 2;
    }
}

The main problem with this is that the middle if-else construct if (nbooksPurchased >= 3 && (nbooksPurchased <= 7)) { is executed for all customers, not only premium customers. So regular customers that buy 3 or 6 books get the 1 free book that only premium customers should have had on such a purchase. If they buy 7 or more, the execution gets into if (ans.equals("n") || ans.equals("N")) { , and you're saved.

The other problem is just a typo, nbooksPurchased >= 3 should have been 5 for premium customers.

Most cases work correctly.

This would be clearer (and hence easier for yourself to correct errors in):

if (isPremiumCustomer) {
    // put if-else for premium customers here
} else {
    // put if-else for regular customers here
}