Chapter 25: BigInteger

Section 25.1: Calculate the First 1,000-Digit Fibonacci Number

Include using System.Numerics and add a reference to System.Numerics to the project.

using System;

using System.Numerics;

namespace Euler_25

{

class Program

{

static void Main(string[] args)

{

BigInteger l1 = 1;

BigInteger l2 = 1; BigInteger current = l1 + l2;

while (current.ToString().Length < 1000)

{

l2 = l1;

l1 = current; current = l1 + l2;

}

Console.WriteLine(current);

}

}

}

This simple algorithm iterates through Fibonacci numbers until it reaches one at least 1000 decimal digits in length, then prints it out. This value is significantly larger than even a ulong could hold.

Theoretically, the only limit on the BigInteger class is the amount of RAM your application can consume.

Note: BigInteger is only available in .NET 4.0 and higher.