I'am programming some software for a bookshop. I have been using 'double' type for entering my ISBN numbers. but recently i found out that sometimes the check-sum character is a roman number 'X'.

How can i 'extend' the definition of what a double character is that it will accept the 'X'? If it is not possible i need to rewrite all my source code so please help me out.

Wow. Using Double is dangerous anyways. A double isn't precise, like ISBN numbers are. You should have at least been using a decimal.

That being said, use a string for an ISBN number. You can't extend double without creating another custom class. Just can't be done. The type is sealed.

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Wow. Using Double is dangerous anyways. A double isn't precise, like ISBN numbers are. You should have at least been using a decimal.

That being said, use a string for an ISBN number. You can't extend double without creating another custom class. Just can't be done. The type is sealed.

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In that case: how can i create a new costum class and adapt the decimal type there?

public class ISBN
{
public double NumericPortion { get; set; }
public string TextPortion { get; set; }

public override string ToString()
{
return TextPortion + NumericPortion;
}
}

?

Use a string instead.

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