/****************************************************************************** * Compilation: javac ISBN.java * Execution: java ISBN n * * Determines the check digit of an ISBN-10 number given the first 9 digits. * * An ISBN-10 number is valid if it consists of 10 digits and * d_1 + 2*d_2 + 3*d_3 + ... + 10*d_10 is a multiple of 11. * For example, 0-201-31452-5 is valid since * 1*5 + 2*2 + 3*5 + 4*4 + 5*1 + 6*3 + 7*1 + 8*0 + 9*2 + 10*0 = 88 * and 88 is a multiple of 11. * * % java ISBN 013407642 * The full ISBN number is 0134076427 * * % java ISBN 067233784 * The full ISBN number is 0672337843 * * % java ISBN 032157351 * The full ISBN number is 032157351X * ******************************************************************************/ public class ISBN { public static void main(String[] args) { // read in one command-line argument int n = Integer.parseInt(args[0]); // compute the weighted sum of the digits, from right to left int sum = 0; for (int i = 2; i <= 10; i++) { int digit = n % 10; // rightmost digit sum = sum + i * digit; n = n / 10; } // print out check digit, use X for 10 System.out.print("The full ISBN number is " + args[0]); if (sum % 11 == 1) System.out.println("X"); else if (sum % 11 == 0) System.out.println("0"); else System.out.println(11 - (sum % 11)); } }