Program for credit card number validation

Write a program that prompts the user to enter a credit card number as a long integer and Display whether that card is valid or invalid.
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

The problem can be solved by using Luhn algorithm. 

Luhn check or the Mod 10 check, which can be described as follows (for illustration, consider the card number 4388576018402626):

• Step 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 (like for 12:1+2, 18=1+8).
• Step 2. Now add all single-digit numbers from Step 1. 
  4 + 4 + 8 + 2 + 3 + 1 + 7 + 8 = 37
• Step 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
• Step 4. Sum the results from Step 2 and Step 3. 37 + 38 = 75
• Step 5. If the result from Step 4 is divisible by 10, the card number is valid; otherwise, it is invalid. 

Examples :

Input : 379354508162306
Output : 379354508162306 is Valid

Input : 4388576018402626
Output : 4388576018402626 is invalid

Implementation:

C++

// C++ program to check if a given credit
// card is valid or not.
#include <iostream>
using namespace std;

// Return this number if it is a single digit, otherwise,
// return the sum of the two digits
int getDigit(int number)
{
  if (number < 9)
    return number;
  return number / 10 + number % 10;
}

// Return the number of digits in d
int getSize(long d)
{
  string num = to_string(d);
  return num.length();
}

// Return the first k number of digits from
// number. If the number of digits in number
// is less than k, return number.
long getPrefix(long number, int k)
{
  if (getSize(number) > k)
  {
    string num = to_string(number);
    return stol(num.substr(0, k));
  }
  return number;
}

// Return true if the digit d is a prefix for number
bool prefixMatched(long number, int d)
{
  return getPrefix(number, getSize(d)) == d;
}

// Get the result from Step 2
int sumOfDoubleEvenPlace(long int number)
{
  int sum = 0;
  string num = to_string(number) ;
  for (int i = getSize(number) - 2; i >= 0; i -= 2)
    sum += getDigit(int(num[i] - '0') * 2);

  return sum;
}

// Return sum of odd-place digits in number
int sumOfOddPlace(long number)
{
  int sum = 0;
  string num = to_string(number) ;
  for (int i = getSize(number) - 1; i >= 0; i -= 2)
    sum += num[i] - '0';
  return sum;
}

// Return true if the card number is valid
bool isValid(long int number)
{
  return (getSize(number) >= 13 &&
          getSize(number) <= 16) &&
    (prefixMatched(number, 4) ||
     prefixMatched(number, 5) ||
     prefixMatched(number, 37) ||
     prefixMatched(number, 6)) &&
    ((sumOfDoubleEvenPlace(number) +
      sumOfOddPlace(number)) % 10 == 0);
}

// Driver Code
int main()
{
  long int number = 5196081888500645L;
  cout << number << " is " <<  (isValid(number) ? "valid" : "invalid");
  return 0;
}

// This code is contributed by yuvraj_chandra

Java

// Java program to check if a given credit
// card is valid or not.
import java.util.Scanner;

public class CreditCard {
    // Main Method
    public static void main(String[] args)
    {
        long number = 5196081888500645L;

        System.out.println(number + " is " +
        (isValid(number) ? "valid" : "invalid"));
    }

    // Return true if the card number is valid
    public static boolean isValid(long number)
    {
       return (getSize(number) >= 13 &&
               getSize(number) <= 16) &&
               (prefixMatched(number, 4) ||
                prefixMatched(number, 5) ||
                prefixMatched(number, 37) ||
                prefixMatched(number, 6)) &&
              ((sumOfDoubleEvenPlace(number) +
                sumOfOddPlace(number)) % 10 == 0);
    }

    // Get the result from Step 2
    public static int sumOfDoubleEvenPlace(long number)
    {
        int sum = 0;
        String num = number + "";
        for (int i = getSize(number) - 2; i >= 0; i -= 2)
            sum += getDigit(Integer.parseInt(num.charAt(i) + "") * 2);

        return sum;
    }

    // Return this number if it is a single digit, otherwise,
    // return the sum of the two digits
    public static int getDigit(int number)
    {
        if (number < 9)
            return number;
        return number / 10 + number % 10;
    }

    // Return sum of odd-place digits in number
    public static int sumOfOddPlace(long number)
    {
        int sum = 0;
        String num = number + "";
        for (int i = getSize(number) - 1; i >= 0; i -= 2)
            sum += Integer.parseInt(num.charAt(i) + "");
        return sum;
    }

    // Return true if the digit d is a prefix for number
    public static boolean prefixMatched(long number, int d)
    {
        return getPrefix(number, getSize(d)) == d;
    }

    // Return the number of digits in d
    public static int getSize(long d)
    {
        String num = d + "";
        return num.length();
    }

    // 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)
    {
        if (getSize(number) > k) {
            String num = number + "";
            return Long.parseLong(num.substring(0, k));
        }
        return number;
    }
}

Python3

class CreditCard:
    # Main Method
    @staticmethod
    def main(args):
        number = 5196081888500645
        print(str(number) + " is " +
              ("valid" if CreditCard.isValid(number) else "invalid"))

    # Return true if the card number is valid
    @staticmethod
    def isValid(number):
        return (CreditCard.getSize(number) >= 13 and CreditCard.getSize(number) <= 16) and (CreditCard.prefixMatched(number, 4) or CreditCard.prefixMatched(number, 5) or CreditCard.prefixMatched(number, 37) or CreditCard.prefixMatched(number, 6)) and ((CreditCard.sumOfDoubleEvenPlace(number) + CreditCard.sumOfOddPlace(number)) % 10 == 0)

    # Get the result from Step 2
    @staticmethod
    def sumOfDoubleEvenPlace(number):
        sum = 0
        num = str(number) + ""
        i = CreditCard.getSize(number) - 2
        while (i >= 0):
            sum += CreditCard.getDigit(int(str(num[i]) + "") * 2)
            i -= 2
        return sum

    # Return this number if it is a single digit, otherwise,
    # return the sum of the two digits
    @staticmethod
    def getDigit(number):
        if (number < 9):
            return number
        return int(number / 10) + number % 10

    # Return sum of odd-place digits in number
    @staticmethod
    def sumOfOddPlace(number):
        sum = 0
        num = str(number) + ""
        i = CreditCard.getSize(number) - 1
        while (i >= 0):
            sum += int(str(num[i]) + "")
            i -= 2
        return sum

    # Return true if the digit d is a prefix for number
    @staticmethod
    def prefixMatched(number,  d):
        return CreditCard.getPrefix(number, CreditCard.getSize(d)) == d

    # Return the number of digits in d
    @staticmethod
    def getSize(d):
        num = str(d) + ""
        return len(num)

    # Return the first k number of digits from
    # number. If the number of digits in number
    # is less than k, return number.
    @staticmethod
    def getPrefix(number,  k):
        if (CreditCard.getSize(number) > k):
            num = str(number) + ""
            return int(num[0:k])
        return number

if __name__ == "__main__":
    CreditCard.main([])

# This code is contributed by Aarti_Rathi

C#

// C# program to check if a given
// credit card is valid or not.
using System;

class CreditCard {

    // Main Method
    public static void Main()
    {
        long number = 5196081888500645L;
        Console.Write(number + " is " +
                     (isValid(number) ?
                     "valid" : "invalid"));
    }

    // Return true if the card number is valid
    public static bool isValid(long number)
    {
    return (getSize(number) >= 13 &&
            getSize(number) <= 16) &&
            (prefixMatched(number, 4) ||
            prefixMatched(number, 5) ||
            prefixMatched(number, 37) ||
            prefixMatched(number, 6)) &&
            ((sumOfDoubleEvenPlace(number) +
            sumOfOddPlace(number)) % 10 == 0);
    }

    // Get the result from Step 2
    public static int sumOfDoubleEvenPlace(long number)
    {
        int sum = 0;
        String num = number + "";
        for (int i = getSize(number) - 2; i >= 0; i -= 2)
            sum += getDigit(int.Parse(num[i] + "") * 2);

        return sum;
    }

    // Return this number if it is a
    // single digit, otherwise, return
    // the sum of the two digits
    public static int getDigit(int number)
    {
        if (number < 9)
            return number;
        return number / 10 + number % 10;
    }

    // Return sum of odd-place digits in number
    public static int sumOfOddPlace(long number)
    {
        int sum = 0;
        String num = number + "";
        for (int i = getSize(number) - 1; i >= 0; i -= 2)
            sum += int.Parse(num[i] + "");
        return sum;
    }

    // Return true if the digit d
    // is a prefix for number
    public static bool prefixMatched(long number, int d)
    {
        return getPrefix(number, getSize(d)) == d;
    }

    // Return the number of digits in d
    public static int getSize(long d)
    {
        String num = d + "";
        return num.Length;
    }

    // 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)
    {
        if (getSize(number) > k)
        {
            String num = number + "";
            return long.Parse(num.Substring(0, k));
        }
        return number;
    }
}

// This code is contributed by nitin mittal.

Javascript

<script>

// JavaScript program to check if a given credit
// card is valid or not.

// Return this number if it is a single digit, otherwise,
// return the sum of the two digits
function getDigit(number)
{
if (number < 9)
    return number;
return Math.floor(number / 10) + number % 10;
}

// Return the number of digits in d
function getSize(d)
{
let num = d.toString();
return num.length;
}

// Return the first k number of digits from
// number. If the number of digits in number
// is less than k, return number.
function getPrefix(number,k)
{
if (getSize(number) > k)
{
    let num = number.toString();
    return parseInt(num.substring(0, k));
}
return number;
}

// Return true if the digit d is a prefix for number
function prefixMatched(number,d)
{
return getPrefix(number, getSize(d)) == d;
}

// Get the result from Step 2
function sumOfDoubleEvenPlace(number)
{
let sum = 0;
let num = number.toString() ;
for (let i = getSize(number) - 2; i >= 0; i -= 2)
    sum += getDigit((num.charCodeAt(i) - '0'.charCodeAt(0)) * 2);

return sum;
}

// Return sum of odd-place digits in number
function sumOfOddPlace(number)
{
let sum = 0;
let num = number.toString();
for (let i = getSize(number) - 1; i >= 0; i -= 2)
    sum += num.charCodeAt(i) - '0'.charCodeAt(0);
return sum;
}

// Return true if the card number is valid
function isValid(number)
{
return (getSize(number) >= 13 &&
        getSize(number) <= 16) &&
    (prefixMatched(number, 4) ||
    prefixMatched(number, 5) ||
    prefixMatched(number, 37) ||
    prefixMatched(number, 6)) &&
    ((sumOfDoubleEvenPlace(number) +
    sumOfOddPlace(number)) % 10 == 0);
}

// Driver Code

let number = 5196081888500645
document.write(number + " is " + (isValid(number) ? "valid" : "invalid"));


// This code is contributed by shinjanpatra

</script>

Output

5196081888500645 is valid

Time Complexity: O(n), where n represents the size of the given string.
Auxiliary Space: O(1), no extra space is required, so it is a constant.