Tyrone

the output should be:
Enter the first 12 digits of an ISBN-13 as a string:978013213080
The ISBN-13 number is 9780132130806
import java.util.Scanner;
public class IBN13 {
public static void main(String[] args){
int d1,d2,d3,d4,d5,d6,d7,d8,d9,d10,d11,d12;
Scanner input = new Scanner(System.in);
String line = input.nextLine();
int[] digit = new int[line.length()];
for(int i = 0; i < digit.length; ++i)
digit[i] = line.charAt(i) - '0';

System.out.print("Enter the 13 digits of the ISBN: ");

int d13 = input.nextInt();

d13 = 10 - ((d1 *1 ) + (d2*3) + (d3*1) + (d4*3) + (d5*1) + (d6*3) +
(d7*1) + (d8*3) + (d9*1) + (d10 * 3) + (d11*1) + (3* d12)) % 10);



if (d13 == 13){


System.out.print ( "ISBN is:" + d1 + d2 + d3 + d4 + d5 + d6 + d7 + d8 +
d9 + "X");

}
else {

System.out.print ( "ISBN is:" + d1 + d2 + d3 + d4 + d5 + d6 + d7 + d8 +
d9 + d10);

}

}

}

Bill

You defined variables d1, d2, d3... but you didn't assign values to any of them.

EddieJ

Maybe you want to replace d1 with digit [0], and d2 with digit [1].

You are never initializing d1, d2, etc.

But since you seem to know how to use an array, you wouldn't want to use d1, d2, etc.

========= NEW CODE ===========
import java.util.Scanner;
public class IBN13 {
public static void main (String [] args) {
Scanner input= new Scanner (System.in);
System.out.println ("input isbn12");
String isbn = input.nextLine ();
System.out.println ("ISBN is " + makeISBN (isbn));
}

static String makeISBN (String isbn) {
char[] isbnChar = isbn.toCharArray ();

if (isbnChar.length != 12) return "to short";
for(int i=0; i<isbnChar.length; i++) {
if (!Character.isDigit(isbnChar[i])) return "not all digits";
}

int sum = 0;
for(int i=0; i<(isbnChar.length-1); i+=2)
sum += Character.getNumericValue (isbnChar [i]);
for (int i=1; i<isbnChar.length; i=i+2)
sum += (Character.getNumericValue (isbnChar [i])*3);
int CheckDigit = 10 - sum%10;
return isbn + CheckDigit;
}
}