Random Constructor (Int32)

 

Initializes a new instance of the Random class, using the specified seed value.

Namespace:   System
Assembly:  mscorlib (in mscorlib.dll)

public:
Random(
	int Seed
)

Parameters

Seed
Type: System::Int32

A number used to calculate a starting value for the pseudo-random number sequence. If a negative number is specified, the absolute value of the number is used.

Providing an identical seed value to different Random objects causes each instance to produce identical sequences of random numbers. This is often done when testing apps that rely on random number generators.

If your application requires different random number sequences, invoke this constructor repeatedly with different seed values. One way to produce a unique seed value is to make it time-dependent. For example, derive the seed value from the system clock, as the Random() overload does. However, the system clock might not have sufficient resolution to provide different invocations of this constructor with a different seed value. This results in random number generators that generate identical sequences of pseudo-random numbers, as illustrated by the first two Random objects in the following example. To prevent this, apply an algorithm to differentiate the seed value in each invocation, or call the Thread::Sleep method to ensure that you provide each constructor with a different seed value.

No code example is currently available or this language may not be supported.

Another option is to instantiate a single Random object that you use to generate all the random numbers in your application. This yields slightly better performance, since instantiating a random number generator is fairly expensive.

The following example creates Random objects with the class constructor that takes a seed parameter and generates a sequence of random integers and doubles. The example illustrates that the same sequence is generated when the Random object is created again with the constructor and seed parameter.

// 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
*/

Universal Windows Platform
Available since 8
.NET Framework
Available since 1.1
Portable Class Library
Supported in: portable .NET platforms
Silverlight
Available since 2.0
Windows Phone Silverlight
Available since 7.0
Windows Phone
Available since 8.1
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