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ISBN Code Program - Java Program

An ISBN (International Standard Book Number) is a ten digit code which uniquely identifies a book.

The first nine digits represent the Group, Publisher and Title of the book and the last digit is used to check whether ISBN is correct or not.

Each of the first nine digits of the code can take a value between 0 and 9. Sometimes it is necessary to make the last digit equal to ten; this is done by writing the last digit of the code as X.

To verify an ISBN, calculate 10 times the first digit, plus 9 times the second digit, plus 8 times the third and so on until we add 1 time the last digit. If the final number leaves no remainder when divided by 11, the code is a valid ISBN.

For example:
1. 0201103311:
10 * 0 + 9 * 2 + 8 * 0 + 7 * 1 + 6 * 1 + 5 * 0 + 4 * 3 + 3 * 3 + 2 * 1 + 1 * 1 = 55.
Since 55 leaves no remainder when divided by 11, hence it is a valid ISBN.
2. 007462542X:
10 * 0 + 9 * 0 + 8 * 7 + 7 * 4 + 6 * 6 + 5 * 2 + 4 * 5 + 3 * 4 + 2 * 2 + 1 * 10 = 176.
Since 176 leaves no remainder when divided by 11, hence it is a valid ISBN.
3. 0112112425:
10 * 0 + 9 * 1 + 8 * 1 + 7 * 2 + 6 * 1 + 5 * 1 + 4 * 2 + 3 * 4 + 2 * 2 + 1 * 5 = 71.
Since 71 leaves a remainder when divided by 11, hence it is not a valid ISBN.

Design a program to accept a ten digit code from the user. For an invalid input, display an appropriate message. Verify the code for its validity in the format specified below:

Test your program with sample data and some random data.

Example 1:
INPUT CODE: 0201530821
OUTPUT:
SUM = 99
LEAVES NO REMAINDER – VALID ISBN CODE

Example 2:
INPUT CODE: 035680324
OUTPUT: INVALID INPUT

Example 3:
INPUT CODE: 0231428031
OUTPUT:
SUM = 122
LEAVES REMAINDER – INVALID ISBN CODE

import java.io.*;
class ISBN{
    public static void main(String args[])throws IOException{
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("ISBN Code: ");
        String isbn = br.readLine();
        isbn = isbn.trim().toUpperCase();
        int len = isbn.length();
        char last = isbn.charAt(len - 1);

        int sum = 0;
        int n = 10;
        if(len != 10){
            System.out.println("INVALID INPUT");
            return;
        }
        if(!(last >= \'0\' && last <= \'9\') && last != \'X\'){
            System.out.println("INVALID INPUT");
            return;
        }

       boolean wrong = false;
        for(int i = 0; i < len - 1; i++){
            char ch = isbn.charAt(i);
            if(!(ch >= \'0\' && ch <= \'9\')){
                wrong = true;
                break;
            }
            else{
                int d = Integer.parseInt(Character.toString(ch));
                sum += d * n;
                n--;
            }
        }

        if(wrong){
            System.out.println("INVALID INPUT");
            return;
        }
        if(last == \'X\')
            sum += 10;
        else
            sum += Integer.parseInt(Character.toString(last));
        System.out.println("SUM = " + sum);
        if(sum % 11 == 0)
            System.out.println("LEAVES NO REMAINDER - VALID ISBN CODE");
        else
            System.out.println("LEAVES REMAINDER - INVALID ISBN CODE");
    }
}

 
OUTPUT 1:

ISBN Code: 0201530821
SUM = 99
LEAVES NO REMAINDER - VALID ISBN CODE

OUTPUT 2:

ISBN Code: 035680324
INVALID INPUT


OUTPUT 3:

ISBN Code: 0231428031
SUM = 122
LEAVES REMAINDER - INVALID ISBN CODE