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Luhn Algorithm

AustinLeath
0 likes • Nov 18, 2022
C#
// C# program to implement
// Luhn algorithm
using System;
class GFG {
// Returns true if given
// card number is valid
static bool checkLuhn(String cardNo)
{
int nDigits = cardNo.Length;
int nSum = 0;
bool isSecond = false;
for (int i = nDigits - 1; i >= 0; i--)
{
int d = cardNo[i] - '0';
if (isSecond == true)
d = d * 2;
// We add two digits to handle
// cases that make two digits
// after doubling
nSum += d / 10;
nSum += d % 10;
isSecond = !isSecond;
}
return (nSum % 10 == 0);
}
// Driver code
static public void Main()
{
String cardNo = "79927398713";
if (checkLuhn(cardNo))
Console.WriteLine("This is a valid card");
else
Console.WriteLine("This is not a valid card");
}
}