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
3.2实现两个大数的加减乘除
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();
}
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