C#实现大数字的运算
1、添加引用：System.Numerics.dll

2、添加命名空间：using System.Numerics;

3、实例：

3.1判断一个数字是不是质数　

复制代码 代码如下:
static void Main(string[] args)
{
Console.WriteLine("请输入一个很大的数字：");
string bigNumber = Console.ReadLine();
BigInteger bigInteger = BigInteger.Parse(bigNumber);
bool isNumber=false;
for (BigInteger i = 2; i < BigInteger.Pow(bigInteger, 2);i++ )
{
if (bigInteger % i == 0)
{
isNumber = true;
break;
}
}
if (isNumber)
{
Console.WriteLine("不是质数");
}
else
{
Console.WriteLine("是质数");
}
Console.ReadLine();
}

3.2实现两个大数的加减乘除

复制代码 代码如下:
static void Main(string[] args)
{
Console.Write("请输入第一个大数字:");
string bigNum1 = Console.ReadLine();
BigInteger bigInt1 = BigInteger.Parse(bigNum1);

Console.Write("请输入第二个大数字:");
string bigNum2 = Console.ReadLine();
BigInteger bigInt2 = BigInteger.Parse(bigNum2);
Console.Write(Environment.NewLine);

BigInteger addNum = bigInt1 + bigInt2;
BigInteger subNum = bigInt1 - bigInt2;
BigInteger purNum = bigInt1 * bigInt2;
BigInteger divNum = bigInt1 / bigInt2;

Console.WriteLine("两大数相加结果为：{0}",addNum);
Console.WriteLine("两大数相减结果为：{0}",subNum);
Console.WriteLine("两大数相乘结果为：{0}",purNum);
Console.WriteLine("两大数相除结果为：{0}",divNum);

Console.ReadLine();
}