Validating Credit Cards Concepts tested by this program: • Variables • Input/out

Question

Validating Credit Cards Concepts tested by this program: • Variables • Input/output • Mathematical Expressions • Loops • Conditional Statements • Strings • Methods Problem Description: 6.31 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 Luhn Check Algorithm: In 1954, Hans Luhn of IBM proposed an algorithm for validating credit card numbers. The algorithm is useful to determine if a card number is entered correctly or if a credit card is scanned correctly by a scanner. Almost all 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. 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. 4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 = 37 3. Add all digits in the odd places from right to left in the card number. 6 + 6 + 0 + 8 + 0 + 7 + 8 + 3 = 38 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. Your objective is to 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. Your class name should be CreditCard and file name should be CreditCard.java 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) /** input credit card’s number from keyboard Return this credit Card’s number */ public static long inputData() /** Display result using a method println() */ public static void displayResult(long number) Here are sample runs of the program: (You may also implement this program by reading the input as a string and processing the string to validate the credit card.) Sample Output: Run 1: Enter a credit card number as a long integer: 4246345689049834 4246345689049834 is invalid Run 2: Enter a credit card number as a long integer: 4388576018410707 4388576018410707 is valid

Explanation / Answer

CreditCardValidator.java

import java.util.Scanner;

public class CreditCardValidator {
   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;
   }
   }
  
   //This method finds the sum of digits of odd places
   public static int SumofOddPlace(long number){
   int result = 0;
   while (number > 0){
   result += (int) (number % 10);
   number = number / 100;
   }
   return result;
   }
   //This method finds the sum of digits by doubling the even places
   public static int SumofDoubleEvenPlace(long number){
  
       //Declaring variables
   int result = 0;
   long temp = 0;
  
   while(number > 0){
   temp = number % 100;
   result += getDigit((int) (temp / 10) * 2);
   number = number / 100;
   }
   return result;
   }
     
   //Based on the prefix number it displays the corresponding card name
   public static boolean prefixMatched(long number, int d){
     
   if ((getPrefix(number, d) == 4)
   || (getPrefix(number, d) == 5)
   || (getPrefix(number, d) == 37)
   ||(getPrefix(number, d) == 6)){
     
   if (getPrefix(number, d) == 4){
   System.out.println(" Visa Card");
   }else if (getPrefix(number, d) == 5){
   System.out.println(" Master Card");
   }else if (getPrefix(number, d) == 37){
   System.out.println(" American Express Card");
   }else if (getPrefix(number, d) == 6){
   System.out.println(" Discover Card");
   }
   return true;
   }else{
   return false;
   }
   }
  
  
   //This method finds the size of the credit card number
   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 class object is used to read the inputs entered by the user
   Scanner key = new Scanner(System.in);
     
     
   //Getting the credit card number entered by the user
   System.out.println("Enter a credit card number");
     
   long input = key.nextLong();
     
   /* If the credit card number is valid the display
   * the valid message if not display invalid message
   */
   if (isValid(input) == true){
   System.out.println(" " + input + " Is valid");
   }else{
   System.out.println(" " + input + " Is not valid");
   }
   }
   }

________________________

output#1:

Enter a credit card number
4388576018410707

Visa Card

4388576018410707 Is valid

___________________

Output#2:

Enter a credit card number
4246345689049834

4246345689049834 Is not valid

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