Shiv Patel Shiv Patel - 2 months ago 30
Java Question

JAVA ISBN-10 Number: Find 10th digit

Question :

An ISBN-10 consists of 10 digits: d1,d2,d3,d4,d5,d6,d7,d8,d9,d10. The last digit, d10, is a checksum,which is calculated from the other nine digits using
the following formula:

(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 ISBN-10
convention.

Write a program that prompts the user to enter the first 9 digits and displays the 10-digit ISBN (including leading zeros). Your program should read the input as an integer.

Here are sample runs:

Enter the first 9 digits of an ISBN as integer: 013601267

The ISBN-10 number is 0136012671

MY CODE:

import java.util.Scanner;

public class ISBN_Number {

public static void main(String[] args) {
Scanner s = new Scanner(System.in);

int[] num = new int[9];

System.out.println("Enter the first 9 digits of the an ISBN as integer: ");

for (int i = 0; i < num.length; i++) {
for (int j = 1; j < 10; j++) {
num[i] = s.nextInt() * j;
}
}

int sum = 0;
for (int a = 0; a < 10; a++) {
sum += num[a];
}
int d10 = (sum % 11);
System.out.println(d10);

if (d10 == 10) {
System.out.println("The ISBN-10 number is " + num + "X");
} else {
System.out.println("The ISBN-10 number is" + num);
}
}
}


ISSUE:
I am new to learning java, hence I am having trouble trying to figure this question out. Can some tell me where I am going wrong because I am not getting the expected outcome. Thank you.

Answer

nextInt() consumes the entire token 013601267, not just a single digit, which was not your plan. A much easier approach could be to consume it as a single string and then iterate over the characters:

String num = s.next();
int sum = 0;
for (int i = 1; i <= num.length(); ++i) {
    sum += (i * num.charAt(i - 1) - '0');
}

int d10 = (sum % 11);
if (d10 == 10) {
    System.out.println("The ISBN-10 number is " + num + "X");
} else {
    System.out.println("The ISBN-10 number is " + num + d10);
}
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