( Financial: credit card number validation ) Credit card numbers follow certain
ID: 3551345 • Letter: #
Question
(Financial: credit card number validation) Credit card numbers follow certain patterns.
A credit card number must have between 13 and 16 digits. It must start with:
? 4 for Visa cards
? 5 for Master cards
? 37 for American Express cards
? 6 for Discover cards
In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers.
The algorithm is useful to determine whether a card number is entered correctly
or whether a credit card is scanned correctly by a scanner. Credit card
numbers are generated following this validity check, commonly known as the
Luhn check or the Mod 10 check, which can be described as follows (for illustration,
consider the card number 4388576018402626):
1. Double every second digit from right to left. If doubling of a digit results in a
two-digit number, add up the two digits to get a single-digit number.
4388576018402626
2 * 2 = 4
2 * 2 = 4
4 * 2 = 8
1 * 2 = 2
6 * 2 = 12 (1 + 2 = 3)
5 * 2 = 10 (1 + 0 = 1)
8 * 2 = 16 (1 + 6 = 7)
4 * 2 = 8
2. Now add all single-digit numbers from Step 1.
3. Add all digits in the odd places from right to left in the card number.
4. Sum the results from Step 2 and Step 3.
37 + 38 = 75
5. If the result from Step 4 is divisible by 10, the card number is valid; otherwise,
it is invalid. For example, the number 4388576018402626 is invalid, but the
number 4388576018410707 is valid.
Write a program that prompts the user to enter a credit card number as a long
integer.
Display whether the number is valid or invalid. Design your program to
use the following methods:
/** Return true if the card number is valid */
public static boolean isValid(long number)
/** Get the result from Step 2 */
public static int sumOfDoubleEvenPlace(long number)
/** Return this number if it is a single digit, otherwise,
* return the sum of the two digits */
public static int getDigit(int number)
/** Return sum of odd-place digits in number */
public static int sumOfOddPlace(long number)
/** Return true if the digit d is a prefix for number */
public static boolean prefixMatched(long number, int d)
/** Return the number of digits in d */
public static int getSize(long d)
/** Return the first k number of digits from number. If the
* number of digits in number is less than k, return number. */
public static long getPrefix(long number, int k)
Here are sample runs of the program:
Enter a credit card number as a long integer:
4388576018410707 is valid
4388576018410707
Enter a credit card number as a long integer:
4388576018402626 is invalid
4388576018402626
**
The most important part is these extra instructions:
In addition to the output listed in the book, your program must ask the user for the amount to be charged. The output will indicate the type of card used (Visa, MasterCard, etc.), the card number and amount charged. However, if the card number is invalid the output will inform the user and ask the user to reenter a valid card number. The user will be given three attempts to enter a valid card number. After a third unsuccessful attempt, the program will inform the user that his/her account has been frozen and to contact customer service for assistance.
After either a successful entry or the user's third unsuccessful attempt, the program will terminate.
Explanation / Answer
import java.util.Scanner;
public class CreditCardValidation {
public static boolean isValid(long number) {
int total = sumOfDoubleEvenPlace(number) + sumOfOddPlace(number);
if ((total % 10 == 0) && (prefixMatched(number, 1) == true) && (getSize(number)>=13 ) && (getSize(number)<=16 )) {
return true;
} else {
return false;
}
}
public static int getDigit(int number) {
if (number <= 9) {
return number;
} else {
int firstDigit = number % 10;
int secondDigit = (int) (number / 10);
return firstDigit + secondDigit;
}
}
public static int sumOfOddPlace(long number) {
int result = 0;
while (number > 0) {
result += (int) (number % 10);
number = number / 100;
}
return result;
}
public static int sumOfDoubleEvenPlace(long number) {
int result = 0;
long temp = 0;
while (number > 0) {
temp = number % 100;
result += getDigit((int) (temp / 10) * 2);
number = number / 100;
}
return result;
}
public static boolean prefixMatched(long number, int d) {
if ((getPrefix(number, d) == 4)
|| (getPrefix(number, d) == 5)
|| (getPrefix(number, d) == 3)) {
if (getPrefix(number, d) == 3) {
System.out.println(" Visa Card ");
} else if (getPrefix(number, d) == 5) {
System.out.println(" Master Card ");
} else if (getPrefix(number, d) == 3) {
System.out.println(" American Express Card ");
}
return true;
} else {
return false;
}
}
public static int getSize(long d) {
int count = 0;
while (d > 0) {
d = d / 10;
count++;
}
return count;
}
public static long getPrefix(long number, int k) {
if (getSize(number) < k) {
return number;
} else {
int size = (int) getSize(number);
for (int i = 0; i < (size - k); i++) {
number = number / 10;
}
return number;
}
}
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
System.out.print("Enter a credit card number as a long integer: ");
long input = sc.nextLong();
if (isValid(input) == true) {
System.out.println(" " + input + " is Valid. ");
} else {
System.out.println(" " + input + " is Invalid. ");
}
}
}
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