using System.Numerics;
计算 斐波那契数列(Fibonacci sequence),不受长整型位数限制。
编写 fibonacci.cs 如下
// C# program for Fibonacci Series
// using Dynamic Programming
using System;
using System.Numerics;class fibonacci {static BigInteger fib(int n){	BigInteger a = new BigInteger(0);BigInteger b = new BigInteger(1);BigInteger c = new BigInteger(0);int i;for (i = 2; i <= n; i++) {c = a + b;a = b;b = c;}return b;}// Fibonacci Series testpublic static void Main(string[] args){if (args.Length <1){Console.WriteLine(" usage: fib.exe n ");return;}       int n;if (int.TryParse(args[0], out n)){if (n >1) Console.WriteLine(fib(n));} else {Console.WriteLine(" input n must be +int ");}}
}
where csc
 C:\Windows\Microsoft.NET\Framework\v4.0.30319\csc.exe
编译  csc fibonacci.cs
 fibonacci.cs(8,9): error CS0246: 未能找到类型或命名空间名称“BigInteger”
 编译  csc  /r:System.Numerics.dll  fibonacci.cs
运行 fibonacci.exe 1000
 参阅:https://www.geeksforgeeks.org/program-for-nth-fibonacci-number/