/******Weekend Programming Challenge –
Week #43 Bank Card validation *********/
Problem:
Bank card numbers are not random, they carry
information for the card processor (Visa/Mastercard etc), bank which issued the
card, the account and checksum. More on the subject is available at http://en.wikipedia.org/wiki/Bank_card_number
Make code which enters card number and validate it
i.e. writes VALID or INVALID number has been entered.
My solution for Arduino:
//Test
number:1234567812345670->ok;1234567812345678-NOK
int test;
void setup()
{
Serial.begin(9600);
Serial.println("This program valid or invalid the code of a credit
card number, according with the Luhn Method.");
Serial.println("Please Write your credit card number in the serial
monitor and push enter.\n");
}
void loop()
{
String
CardNumber="";
if(Serial.available())//Wait until something is writen in the serial
port
{ //Reading
the message from the serial port
delay(100);
while(Serial.available()>0)
CardNumber.concat((char)Serial.read());
Serial.print("Card Number introduced: ");
Serial.println(CardNumber);
test=luhn(CardNumber);
Serial.print("The number: ");
Serial.print(CardNumber);
if(test==0)
Serial.println(" is VALID.");
else
Serial.println(" is INVALID.");
Serial.println();
}
}
/************************************************************************************************************
The Luhn test is used by some credit card companies to
distinguish valid credit card numbers from what could be a random selection of
digits.
Those companies using credit card numbers that can be
validated by the Luhn test have numbers that pass the following test:
1. Reverse
the order of the digits in the number.
2. Take the
first, third, ... and every other odd digit in the reversed digits and sum them
to form the partial sum s1
3. Taking the
second, fourth ... and every other even digit in the reversed digits:
1.
Multiply each digit by two and sum the digits if the answer is greater than
nine to form partial sums for the even digits
2. Sum the
partial sums of the even digits to form s2
1. If s1 + s2
ends in zero then the original number is in the form of a valid cre
************************************************************************************************************/
int luhn(String number)
{
int
numberlength=number.length();
char
charBuf[numberlength+1];//I add one more because I've to take account the end
of string('\0')
char
copyBuf[numberlength+1];
int
odd=0,even=0,sum=0,checkdigit=0;//Variable that help me in the the process of
calculation the validation number
//String to
char array
number.toCharArray(charBuf,numberlength+1);//This
array has the account number in char
Serial.print("Reverse the order of the
digits: ");
for(int
i=0;i<numberlength;i++)
{
copyBuf[i]=charBuf[numberlength-1-i];
Serial.print(copyBuf[i]);
}
Serial.println("\n'Double the digits in
the odd position of the array and if they are bigger than 9 I must sum the two
digits between them.'");
Serial.print("Array of digits: ");
for(int
i=0;i<numberlength;i++)
{
if(i%2!=0)
{
odd=(((int)copyBuf[i])-48)*2;//I sustract 48 for passing char to int
according to the ASCII table
if(odd>9)
odd=1+(odd-10);
copyBuf[i]=odd;
Serial.print(odd);
sum+=odd;
}
else
{
even=((int)copyBuf[i]-48);//char to int
copyBuf[i]=even;
Serial.print(even);
sum+=even;
}
}
Serial.print("\nSum of all these digits:
"); Serial.println(sum);
Serial.print("Multiply the sum by 9:
"); Serial.println(sum*=9);
checkdigit=sum%10;
Serial.print("The last digit is the check
digit: "); Serial.println(checkdigit);
Serial.println("The check digit must be 0
for be valid,else will be invalid");
return checkdigit;
}
