Random Class
Assembly: mscorlib (in mscorlib.dll)
Pseudo-random numbers are chosen with equal probability from a finite set of numbers. The chosen numbers are not completely random because a definite mathematical algorithm is used to select them, but they are sufficiently random for practical purposes. The current implementation of the Random class is based on Donald E. Knuth's subtractive random number generator algorithm. For more information, see D. E. Knuth. "The Art of Computer Programming, volume 2: Seminumerical Algorithms". Addison-Wesley, Reading, MA, second edition, 1981.
The random number generation starts from a seed value. If the same seed is used repeatedly, the same series of numbers is generated. One way to produce different sequences is to make the seed value time-dependent, thereby producing a different series with each new instance of Random. By default, the parameterless constructor of the Random class uses the system clock to generate its seed value, while its parameterized constructor can take an Int32 value based on the number of ticks in the current time.
However, because the clock has finite resolution, creating different Random objects in close succession creates random number generators that produce identical sequences of random numbers. This problem can be avoided by creating a single Random object rather than multiple ones.
To improve performance, create one Random to generate many random numbers over time, instead of repeatedly creating a new Random to generate one random number.
To generate a cryptographically secure random number suitable for creating a random password, for example, use a class derived from System.Security.Cryptography.RandomNumberGenerator such as System.Security.Cryptography.RNGCryptoServiceProvider.
Notes to Inheritors: In the .NET Framework versions 1.0 and 1.1, a minimum implementation of a class derived from Random required overriding the Sample method to define a new or modified algorithm for generating random numbers. The derived class could then rely on the base class implementation of the Random.Next, Random.Next(Int32), Random.Next(Int32,Int32), NextBytes, and NextDouble methods to call the derived class implementation of the Sample method. In the .NET Framework version 2.0 and later, the behavior of the Random.Next, Random.Next(Int32,Int32), and NextBytes methods have changed so that these methods do not necessarily call the derived class implementation of the Sample method. As a result, classes derived from Random that target the .NET Framework 2.0 and later should also override these three methods.The following code example creates Random objects with different overloads of the class constructor and generates sequences of random integers and doubles from the objects.
// Example of the Random class constructors and Random::NextDouble( ) // method. using namespace System; using namespace System::Threading; // Generate random numbers from the specified Random object. void RunIntNDoubleRandoms( Random^ randObj ) { // Generate the first six random integers. for ( int j = 0; j < 6; j++ ) Console::Write( " {0,10} ", randObj->Next() ); Console::WriteLine(); // Generate the first six random doubles. for ( int j = 0; j < 6; j++ ) Console::Write( " {0:F8} ", randObj->NextDouble() ); Console::WriteLine(); } // Create a Random object with the specified seed. void FixedSeedRandoms( int seed ) { Console::WriteLine( "\nRandom numbers from a Random object with seed = {0}:", seed ); Random^ fixRand = gcnew Random( seed ); RunIntNDoubleRandoms( fixRand ); } // Create a random object with a timer-generated seed. void AutoSeedRandoms() { // Wait to allow the timer to advance. Thread::Sleep( 1 ); Console::WriteLine( "\nRandom numbers from a Random object " "with an auto-generated seed:" ); Random^ autoRand = gcnew Random; RunIntNDoubleRandoms( autoRand ); } int main() { Console::WriteLine( "This example of the Random class constructors and Random" "::NextDouble( ) \ngenerates the following output.\n" ); Console::WriteLine( "Create Random objects, and then generate and " "display six integers and \nsix doubles from each." ); FixedSeedRandoms( 123 ); FixedSeedRandoms( 123 ); FixedSeedRandoms( 456 ); FixedSeedRandoms( 456 ); AutoSeedRandoms(); AutoSeedRandoms(); AutoSeedRandoms(); } /* This example of the Random class constructors and Random::NextDouble( ) generates the following output. Create Random objects, and then generate and display six integers and six doubles from each. Random numbers from a Random object with seed = 123: 2114319875 1949518561 1596751841 1742987178 1586516133 103755708 0.01700087 0.14935942 0.19470390 0.63008947 0.90976122 0.49519146 Random numbers from a Random object with seed = 123: 2114319875 1949518561 1596751841 1742987178 1586516133 103755708 0.01700087 0.14935942 0.19470390 0.63008947 0.90976122 0.49519146 Random numbers from a Random object with seed = 456: 2044805024 1323311594 1087799997 1907260840 179380355 120870348 0.21988117 0.21026556 0.39236514 0.42420498 0.24102703 0.47310170 Random numbers from a Random object with seed = 456: 2044805024 1323311594 1087799997 1907260840 179380355 120870348 0.21988117 0.21026556 0.39236514 0.42420498 0.24102703 0.47310170 Random numbers from a Random object with an auto-generated seed: 1624372556 1894939458 302472229 588108304 23919954 1085111949 0.14595512 0.30162298 0.92267372 0.55707657 0.25430079 0.74143239 Random numbers from a Random object with an auto-generated seed: 2105952511 1753605347 280739490 876793040 1129567796 524571616 0.62652210 0.31846701 0.15984073 0.24458755 0.62160607 0.54857684 Random numbers from a Random object with an auto-generated seed: 440048819 1612271236 259006751 1165477776 87731991 2111514930 0.10708907 0.33531104 0.39700773 0.93209853 0.98891135 0.35572129 */
Windows 98, Windows Server 2000 SP4, Windows CE, Windows Millennium Edition, Windows Mobile for Pocket PC, Windows Mobile for Smartphone, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition
The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.