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Random.NextDouble Method

Updated: October 2010

Returns a random number between 0.0 and 1.0.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)
public virtual double NextDouble()

Return Value

Type: System.Double
A double-precision floating point number greater than or equal to 0.0, and less than 1.0.

This method is the public version of the protected method, Sample.

The following example uses the NextDouble method to generate sequences of random doubles.


// Example of the Random class constructors and Random.NextDouble( ) 
// method.
using System;
using System.Threading;

public class Example
{
   // Generate random numbers from the specified Random object.
   static void RunIntNDoubleRandoms(System.Windows.Controls.TextBlock outputBlock, Random randObj)
   {
      // Generate the first six random integers.
      for (int j = 0; j < 6; j++)
         outputBlock.Text += String.Format(" {0,10} ", randObj.Next());
      outputBlock.Text += "\n";

      // Generate the first six random doubles.
      for (int j = 0; j < 6; j++)
         outputBlock.Text += String.Format(" {0:F8} ", randObj.NextDouble());
      outputBlock.Text += "\n";
   }

   // Create a Random object with the specified seed.
   static void FixedSeedRandoms(System.Windows.Controls.TextBlock outputBlock, int seed)
   {
      outputBlock.Text += String.Format(
          "\nRandom numbers from a Random object with " +
          "seed = {0}:", seed) + "\n";
      Random fixRand = new Random(seed);

      RunIntNDoubleRandoms(outputBlock, fixRand);
   }

   // Create a random object with a timer-generated seed.
   static void AutoSeedRandoms(System.Windows.Controls.TextBlock outputBlock)
   {
      // Wait to allow the timer to advance.
      Thread.Sleep(1);

      outputBlock.Text += String.Format(
          "\nRandom numbers from a Random object " +
          "with an auto-generated seed:") + "\n";
      Random autoRand = new Random();

      RunIntNDoubleRandoms(outputBlock, autoRand);
   }

   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      outputBlock.Text += String.Format(
          "This example of the Random class constructors and " +
          "Random.NextDouble( ) \n" +
          "generates the following output.\n") + "\n";
      outputBlock.Text += String.Format(
          "Create Random objects, and then generate and " +
          "display six integers and \nsix doubles from each.") + "\n";

      FixedSeedRandoms(outputBlock, 123);
      FixedSeedRandoms(outputBlock, 123);

      FixedSeedRandoms(outputBlock, 456);
      FixedSeedRandoms(outputBlock, 456);

      AutoSeedRandoms(outputBlock);
      AutoSeedRandoms(outputBlock);
      AutoSeedRandoms(outputBlock);
   }
}

/*
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:
  380213349   127379247  1969091178  1983029819  1963098450  1648433124
 0.08824121  0.41249688  0.36445811  0.05637512  0.62702451  0.49595560

Random numbers from a Random object with an auto-generated seed:
  861793304  2133528783  1947358439   124230908   921262645  1087892791
 0.56880819  0.42934091  0.60162512  0.74388610  0.99432979  0.30310005

Random numbers from a Random object with an auto-generated seed:
 1343373259  1992194672  1925625700   412915644  2026910487   527352458
 0.04937517  0.44618494  0.83879212  0.43139707  0.36163507  0.11024451
*/


The following example calls the NextDouble method to generate 100 random numbers and displays their frequency distribution.


using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      int[] frequency = new int[10];
      double number;
      Random rnd = new Random();

      for (int ctr = 0; ctr <= 99; ctr++)
      {
         number = rnd.NextDouble();
         frequency[(int)Math.Floor(number * 10)]++;
      }
      outputBlock.Text += "Distribution of Random Numbers:" + "\n";
      for (int ctr = frequency.GetLowerBound(0); ctr <= frequency.GetUpperBound(0); ctr++)
         outputBlock.Text += String.Format("0.{0}0-0.{0}9       {1}", ctr, frequency[ctr]) + "\n";
   }
}
// The following example displays output similar to the following:
//       Distribution of Random Numbers:
//       0.00-0.09       16
//       0.10-0.19       8
//       0.20-0.29       8
//       0.30-0.39       11
//       0.40-0.49       9
//       0.50-0.59       6
//       0.60-0.69       13
//       0.70-0.79       6
//       0.80-0.89       9
//       0.90-0.99       14


Silverlight

Supported in: 5, 4, 3

Silverlight for Windows Phone

Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0

XNA Framework

Supported in: Xbox 360, Windows Phone OS 7.0

For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.

Date

History

Reason

October 2010

Added a second example.

Customer feedback.

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