In which data type can I store a 128-bit data in c#?

For example

dataType bit128 = 340282366920938463463374607431768211455;

what will be the datatype?

>Solution :

You should consider using BigInteger

https://docs.microsoft.com/en-us/dotnet/api/system.numerics.biginteger?redirectedfrom=MSDN&view=net-6.0

The BigInteger type is an immutable type that represents an
arbitrarily large integer whose value in theory has no upper or lower
bounds."

string positiveString = "91389681247993671255432112000000";
string negativeString = "-90315837410896312071002088037140000";
BigInteger posBigInt = 0;
BigInteger negBigInt = 0;

try {
   posBigInt = BigInteger.Parse(positiveString);
   Console.WriteLine(posBigInt);
}
catch (FormatException)
{
   Console.WriteLine("Unable to convert the string '{0}' to a BigInteger value.",
                     positiveString);
}

if (BigInteger.TryParse(negativeString, out negBigInt))
  Console.WriteLine(negBigInt);
else
   Console.WriteLine("Unable to convert the string '{0}' to a BigInteger value.",
                      negativeString);

// The example displays the following output:
//   9.1389681247993671255432112E+31
//   -9.0315837410896312071002088037E+34