艾伟_转载：.NET 4.0 Beta2中的BigInteger和Complex类

.NET4.0 Beta2中提供了新的System.Numerics命名空间，对应于System.Numerics.dll。该命名空间下就两个类BigInteger和Complex，我们来简单了解下
这两个类的用法。

BigInteger：任意大小的带符号整数

1.Int64, SByte, UInt16, UInt32, and UInt64这些都有一个MinValue和MaxValue属性。而BigInteger没有这两个属性，因为它没有大小限制。
2.不可变的类型.
3.由于他没有大小限制，理论上当它足够大的时候会出现OutOfMemoryException异常.

BigInteger初始化

1.我们可以使用已有的数据类型来初始化BigInteger，如下：

BigInteger bigIntFromDouble = new BigInteger(179032.6541);//会截取小点前的BigInteger bigIntFromInt64 = new BigInteger(934157136952);

2.我们也可以使用超出现有数据类型范围的方式来得到BigInteger：

byte[] bytes = { 5, 4, 3, 2, 1 };BigInteger number = new BigInteger(bytes);Console.WriteLine("The value of number is {0} (or 0x{0:x}).", number); //The value of number is 4328719365 (or 0x102030405).   字节数组的第一个元素为16进制的最低位，依次升高.

3.可以使用Parse或 TryParse方法将string的实例化为BigInteger：

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

posBigInt = BigInteger.Parse(positiveString);Console.WriteLine(posBigInt);

BigInteger.TryParse(negativeString, out negBigInt);Console.WriteLine(negBigInt);

4. 还可以使用静态方法Pow如下：

BigInteger number = BigInteger.Pow(Int64.MaxValue, 3);

BigInteger支持所有的数学运算，我们可以完全象使用其他整数类型一样使用BigInteger

Complex复数类

1.var z1 = new Complex(); // this creates complex zero (0, 0)  var z2 = new Complex(2, 4);var z3 = new Complex(3, 5);

Console.WriteLine("Complex zero: " + z1);Console.WriteLine(z2 + " + " + z3 + " = " + (z2 + z3));

Console.WriteLine("|z2| = " + z2.Magnitude);Console.WriteLine("Phase of z2 = " + z2.Phase);

2.我们可以使用一个ComplexFormatter类来辅助我们做格式化输出，如下：

using System;using System.Numerics;

public class ComplexFormatter :IFormatProvider, ICustomFormatter{public object GetFormat(Type formatType)    {   if (formatType == typeof(ICustomFormatter))return this;else         return null;   }

public string Format(string format, object arg, IFormatProvider provider)   {if (arg is Complex)      {Complex c1 = (Complex) arg; // Check if the format string has a precision specifier.int precision;string fmtString = String.Empty;if (format.Length > 1) {try {               precision = Int32.Parse(format.Substring(1));            }catch (FormatException) {               precision = 0;            }            fmtString = "N" + precision.ToString();         }if (format.Substring(0, 1).Equals("I", StringComparison.OrdinalIgnoreCase))return c1.Real.ToString("N2") + " + " + c1.Imaginary.ToString("N2") + "i";else if (format.Substring(0, 1).Equals("J", StringComparison.OrdinalIgnoreCase))return c1.Real.ToString("N2") + " + " + c1.Imaginary.ToString("N2") + "j";else            return c1.ToString(format, provider);      }else{if (arg is IFormattable)return ((IFormattable) arg).ToString(format, provider);else if (arg != null) return arg.ToString();else            return String.Empty;      }                           }}

3.使用如下：

Complex c1 = new Complex(12.1, 15.4);Console.WriteLine("Formatting with ToString():" + c1.ToString());Console.WriteLine("Formatting with ToString(format): " +  c1.ToString("N2"));Console.WriteLine("Custom formatting with I0:" +  String.Format(new ComplexFormatter(), "{0:I0}", c1));Console.WriteLine("Custom formatting with J3:" +  String.Format(new ComplexFormatter(), "{0:J3}", c1));