C # generate modulo 10 test bit

The following excerpt from the Wikipedia "http://zh.wikipedia.org/wiki/Luhn%E7%AE%97%E6%B3%95" Luhn algorithm (Luhn algorithm), also known as the "modulo" (Mod 10) algorithm, is a simple checksum algorithm, generally used to verify the identification code, such as the issuing bank identification code, International mobile Device Identification Code (IMEI), the United States to provide a trademark identification number, or Canada Social Security number. This algorithm is now in the public domain and has been widely used, it is not a secure cryptographic hash function, it is designed to prevent accidental errors rather than malicious attacks. Description The Luhn algorithm validates a string of numbers with a checksum, which is usually appended to the end of the string to obtain a complete identification number. We take the number "7992739871" as an example to calculate its check digit: 1.starting from the check digit, from right to left, and even digit by 2 (for example, 7*2=14), the No. 0 bit is also counted as an even digit, and then the two digit digit is added to the 10-bit value (for example, 10:1+0=1,14:1+4=5);2. Add the resulting figures (in this case, in the example);3. The number and modulus 10 (in this case 7), and then 10 de minus (in this case, 3), to obtain a check digit. 4. If the check bit is 10, then take 0 (actually the number and is 10; searched the internet for a lap and found no one mentioned it)

Original number	7	9	9	2	7	3	9	8	7	1	X
Even digit multiply by 2	7	18	9	4	7	6	9	16	7	2	X
Add a number	7	9	9	4	7	6	9	7	7	2	=67

5. Implementing the Code

public static int Getluhn (String str)

{

int n = 0;

int ilen = str. Length;

for (int j = Ilen; j > 0; j--)

{

if ((ilen-j)% 2 = = 0)//even digit

{

int snum = Int. Parse (Str[j-1]. ToString ()) * 2;//even digits multiplied by 2

10-bit value + single digit value

string s = snum.tostring ();

int s1 = 0;

if (s.length = = 2)

S1 = Int. Parse (S[0]. ToString ()) + Int. Parse (S[1]. ToString ());

Else

S1 = Int. Parse (S[0]. ToString ());

n = n + s1;

}

Else

{

n = n + int. Parse (Str[j-1]. ToString ());

}

}

n = ten-(n% 10);

if (n = = 10)

n = 0;

return n;

}

C # generate modulo 10 test bit