字符串长度未正确打印，前面为 0

Question

I'm working on a program that will ask for the first 9 digits of an ISBN number ( d1d2d3d4d5d6d7d8d9 ) that the user inputs and then prints out the number with a 10 th digit based on an equation:

(d1 × 1 + d2 × 2 + d3 × 3 + d4 × 4 + d5 × 5 + d6 × 6 + d7 × 7 + d8 × 8 + d9 × 9)%11)

If the checksum is 10 , the last digit is denoted as X according to the problem. If not, the last number is added onto the ISBN. I have the program working other than when the integer begins with a 0 when entered by the user.

Ex

Input: 113601267
Output: 113601267 6

Ex.

Input: 013032342
Output: "This is an invalid ISBN Entry!"

Here's my code:

int ISBN, r, i;
String st;

Scanner keyboard;
keyboard = new Scanner(System.in);

System.out.println("Please enter the first 9 digits of your ISBN number:");
ISBN = keyboard.nextInt();

st = ("" + ISBN);

if (st.length() == 9){
    r = (st.charAt(0) * 1 + st.charAt(1) * 2 + st.charAt(2) * 3 + st.charAt(3) * 4 + st.charAt(4) * 5 + st.charAt(5) * 6 + st.charAt(6) * 7 + st.charAt(7) * 8 + st.charAt(8) * 9);

    if (r % 11 == 10){
        System.out.println("Your ISBN Number is: " + ISBN + "X");
    }
    else {
        System.out.println(st);
        i = (ISBN * 10) + (r % 11);
        System.out.println("Your ISBN Number is: " + i);
    }   
}
else {
    System.out.println("This is an invalid ISBN entry!");
}

Where did I mess up, or what is going on?

Answer 1

You have two bugs:

1. You should reformat your String to prepend 0 if needed.

2. You have Strings . A String is composed of char s. If your first ISBN digit is 1 , you'll actually do '1'*1 . Since '1' is a char, you'll get the int value of the char , which is 49 . What you have to do is subtract '0' from each char to get the actual int value of each char:

    int ISBN, r, i; String st; Scanner keyboard; keyboard = new Scanner(System.in); System.out.println("Please enter the first 9 digits of your ISBN number:"); ISBN = keyboard.nextInt(); st = String.format("%09d", ISBN); // fixes your 0-bug. if (st.length() == 9){ r = ((st.charAt(0) - '0') * 1 // fixes your computation bug. + (st.charAt(1) - '0') * 2 + (st.charAt(2) - '0') * 3 + (st.charAt(3) - '0') * 4 + (st.charAt(4) - '0') * 5 + (st.charAt(5) - '0') * 6 + (st.charAt(6) - '0') * 7 + (st.charAt(7) - '0') * 8 + (st.charAt(8) - '0') * 9); if (r % 11 == 10){ System.out.println("Your ISBN Number is: " + ISBN + "X"); } else { System.out.println(st); i = (ISBN * 10) + (r % 11); System.out.println("Your ISBN Number is: " + i); } } else { System.out.println("This is an invalid ISBN entry!"); }

   }

Answer 2

ISBN is more of a string than a number.

Have you tried this?

ISBN = keyboard.nextLine();

or

st = keyboard.nextLine();