How to Parse string into BigInteger?

Question

I'm writing my magistracy work in cryptography, and today I was trying to get a BigInteger number from the string. But the only way I find to get BigInteger number from the string was

UTF8Encoding Encoding = new UTF8Encoding();
var bytes = Encoding.GetBytes(myString);
var myBigInteger = new BigInteger(bytes);

But this is not that way I need. I need something which will return me exactly BigInteger representation of the string. For example, if I have

var myString = "1234567890";

I want my BigInteger to be

BigInteger bi = 1234567890;

I've changed title to match your question (was: "how to get string from BigInteger", which looks complete opposite from the post)... — Alexei Levenkov
– Alexei Levenkov, Commented Jun 11, 2013 at 21:17

Geeky Guy · Accepted Answer · 2013-06-11 20:56:24Z

6

You could use that type's Parse method.

BigInteger.Parse(string value)

It's static. You pass a string and get the corresponding value.

For example:

BigInteger reallyBigNumber = BigInteger.Parse("12347534159895123");

answered Jun 11, 2013 at 20:56

Geeky Guy

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1 Comment

Art713 Over a year ago

Thank you! I forget about this at all =)

Abe Miessler · Accepted Answer · 2013-06-11 20:58:10Z

1

I think TryParse is the way you want to go:

BigInteger number1;
bool succeeded1 = BigInteger.TryParse("-12347534159895123", out number1);

This will not throw an exception if you pass an invalid value. It will just set the number to 0 if the input string will not convert. I believe it is faster than Parse as well.

http://msdn.microsoft.com/en-us/library/dd268301.aspx

answered Jun 11, 2013 at 20:58

Abe Miessler

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6 Comments

Geeky Guy Over a year ago

It shoudn't be faster, since it uses Parse internally. It basically uses a try-catch block, returning true in the try block and false in the catch.

Art713 Over a year ago

@Abe Why do you think that TryParse is faster than Parse method?

Abe Miessler Over a year ago

I read it somewhere a while back. Here is an excellent SO question where the accepted answer actually shows the difference in performance: stackoverflow.com/questions/150114/…

Abe Miessler Over a year ago

@Renan, do you have any sources that you could post backing up what you are saying? Not trying to be a smart ass, just curious to see where you are getting this.

Geeky Guy Over a year ago

@AbeMiessler while fidgeting with ILSpy a long time ago I noticed a pattern for all numeric types. I might be wrong, and unfortunately it seems that the latest .NET source codes made available by Microsoft don't include this type. So I can't back up what I said :( please disregard it.

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Tim B · Accepted Answer · 2013-06-11 20:57:33Z

0

BigInteger bi = BigInteger.Parse("1234567890");

answered Jun 11, 2013 at 20:57

Tim B

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