public override char CalculateCheckDigit()
{
byte[] isbnDigits = ValueWithoutHyphens.Select(c => byte.Parse(c.ToString())).ToArray();
int m = 1, result = 0;
for (int i = 0; i < 13; i++)
{
result += isbnDigits[i] * (2 * (m++ % 2) + 1);
}
int checkDigit = (10 - result % 10) % 10;
return(Convert.ToChar(checkDigit));
}
public override char CalculateCheckDigit()
{
byte[] isbnDigits = ValueWithoutHyphens.Select(c => byte.Parse(c.ToString())).ToArray();
int m = 10, result = 0;
for (int i = 0; i < 10; i++)
{
result += isbnDigits[i] * m--;
}
int checkDigit = 11 - (result % 11);
if (checkDigit == 11)
{
return('0');
}
if (checkDigit == 10)
{
return('X');
}
return(Convert.ToChar(checkDigit));
}
