multiply very big integer in .NET

Question

Assume that you have big integers like 1253999939979969998746 and 9999999999. Is there anyway to multiply these big integers in C#?

Note: I've tried System.Numerics.BigInteger class constructor compiler says that integer is too long.

What's your suggestion?

p.s warn me if this question out of topics.

Answer 1

You need to use BigInteger.Parse.

BigInteger num = BigInteger.Parse("1253999939979969998746");

If you try to use an integer value like below

BigInteger num = 1253999939979969998746;

the right hand side needs to have a type, which by default will be an Int32 or a long. But since the number is too large to be an Int32 or a long, the conversion fails, hence the error you get.

As Tim Schmelter pointed out in a comment, to then do your multiplication, you can do the following:

BigInteger num = BigInteger.Multiply(BigInteger.Parse("1253999939979969998746"), 
                                     BigInteger.Parse("9999999999"));