[superkb10]

Hello, I'm writing a program right now that requires some random number generation. I don't actually need any help with code or anything, I'm just a little curious as to how the number generators actually work since a computer can't really generate completely random numbers,so how do they actually work? Again, not needing any real help or anything, I'm just a little curious

[Ryano121]

There's a bit of information on how the Random class works on the MSDN page

There are also many pages scattered around with lots more in depth information on pseudo random number generation if you can handle the math behind it.

[RexGrammer]

If you're interested you can look at the actual code of the .NET Random class:

NOTE: It's somewhat long so I put it in a spoiler tag.

Spoiler

// ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*============================================================
** 
** Class:  Random 
**
** 
** Purpose: A random number generator.
**
**
===========================================================*/ 
namespace System {
 
    using System; 
    using System.Runtime.CompilerServices;
    using System.Globalization; 
[System.Runtime.InteropServices.ComVisible(true)]
    [Serializable()] public class Random {
      //
      // Private Constants 
      //
      private const int MBIG =  Int32.MaxValue; 
      private const int MSEED = 161803398; 
      private const int MZ = 0;
 

      //
      // Member Variables
      // 
      private int inext, inextp;
      private int[] SeedArray = new int[56]; 
 
      //
      // Public Constants 
      //

      //
      // Native Declarations 
      //
 
      // 
      // Constructors
      // 

      public Random()
        : this(Environment.TickCount) {
      } 

      public Random(int Seed) { 
        int ii; 
        int mj, mk;
 
        //Initialize our Seed array.
        //This algorithm comes from Numerical Recipes in C (2nd Ed.)
        mj = MSEED - Math.Abs(Seed);
        SeedArray[55]=mj; 
        mk=1;
        for (int i=1; i<55; i++) {  //Apparently the range [1..55] is special (Knuth) and so we're wasting the 0'th position. 
          ii = (21*i)%55; 
          SeedArray[ii]=mk;
          mk = mj - mk; 
          if (mk<0) mk+=MBIG;
          mj=SeedArray[ii];
        }
        for (int k=1; k<5; k++) { 
          for (int i=1; i<56; i++) {
        SeedArray[i] -= SeedArray[1+(i+30)%55]; 
        if (SeedArray[i]<0) SeedArray[i]+=MBIG; 
          }
        } 
        inext=0;
        inextp = 21;
        Seed = 1;
      } 

      // 
      // Package Private Methods 
      //
 
      /*====================================Sample====================================
      **Action: Return a new random number [0..1) and reSeed the Seed array.
      **Returns: A double [0..1)
      **Arguments: None 
      **Exceptions: None
      ==============================================================================*/ 
      protected virtual double Sample() { 
          //Including this division at the end gives us significantly improved
          //random number distribution. 
          return (InternalSample()*(1.0/MBIG));
      }

      private int InternalSample() { 
          int retVal;
          int locINext = inext; 
          int locINextp = inextp; 

          if (++locINext >=56) locINext=1; 
          if (++locINextp>= 56) locINextp = 1;

          retVal = SeedArray[locINext]-SeedArray[locINextp];
 
          if (retVal<0) retVal+=MBIG;
 
          SeedArray[locINext]=retVal; 

          inext = locINext; 
          inextp = locINextp;

          return retVal;
      } 

      // 
      // Public Instance Methods 
      //
 

      /*=====================================Next=====================================
      **Returns: An int [0..Int32.MaxValue)
      **Arguments: None 
      **Exceptions: None.
      ==============================================================================*/ 
      public virtual int Next() { 
        return InternalSample();
      } 

      private double GetSampleForLargeRange() {
          // The distribution of double value returned by Sample
          // is not distributed well enough for a large range. 
          // If we use Sample for a range [Int32.MinValue..Int32.MaxValue)
          // We will end up getting even numbers only. 
 
          int result = InternalSample();
          // Note we can't use addition here. The distribution will be bad if we do that. 
          bool negative = (InternalSample()%2 == 0) ? true : false;  // decide the sign based on second sample
          if( negative) {
              result = -result;
          } 
          double d = result;
          d += (Int32.MaxValue - 1); // get a number in range [0 .. 2 * Int32MaxValue - 1) 
          d /= 2*(uint)Int32.MaxValue - 1  ; 
          return d;
      } 


      /*=====================================Next=====================================
      **Returns: An int [minvalue..maxvalue) 
      **Arguments: minValue -- the least legal value for the Random number.
      **           maxValue -- One greater than the greatest legal return value. 
      **Exceptions: None. 
      ==============================================================================*/
      public virtual int Next(int minValue, int maxValue) { 
          if (minValue>maxValue) {
              throw new ArgumentOutOfRangeException("minValue",String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Argument_MinMaxValue"), "minValue", "maxValue"));
          }
 
          long range = (long)maxValue-minValue;
          if( range <= (long)Int32.MaxValue) { 
              return ((int)(Sample() * range) + minValue); 
          }
          else { 
              return (int)((long)(GetSampleForLargeRange() * range) + minValue);
          }
      }
 

      /*=====================================Next===================================== 
      **Returns: An int [0..maxValue) 
      **Arguments: maxValue -- One more than the greatest legal return value.
      **Exceptions: None. 
      ==============================================================================*/
      public virtual int Next(int maxValue) {
          if (maxValue<0) {
              throw new ArgumentOutOfRangeException("maxValue", String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("ArgumentOutOfRange_MustBePositive"), "maxValue")); 
          }
          return (int)(Sample()*maxValue); 
      } 

 
      /*=====================================Next=====================================
      **Returns: A double [0..1)
      **Arguments: None
      **Exceptions: None 
      ==============================================================================*/
      public virtual double NextDouble() { 
        return Sample(); 
      }
 

      /*==================================NextBytes===================================
      **Action:  Fills the byte array with random bytes [0..0x7f].  The entire array is filled.
      **Returns:Void 
      **Arugments:  buffer -- the array to be filled.
      **Exceptions: None 
      ==============================================================================*/ 
      public virtual void NextBytes(byte [] buffer){
        if (buffer==null) throw new ArgumentNullException("buffer"); 
        for (int i=0; i<buffer.Length; i++) {
          buffer[i]=(byte)(InternalSample()%(Byte.MaxValue+1));
        }
      } 
    }
 
 

} 
// ==++== 
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--== 
/*============================================================
** 
** Class:  Random 
**
** 
** Purpose: A random number generator.
**
**
===========================================================*/ 
namespace System {
 
    using System; 
    using System.Runtime.CompilerServices;
    using System.Globalization; 
[System.Runtime.InteropServices.ComVisible(true)]
    [Serializable()] public class Random {
      //
      // Private Constants 
      //
      private const int MBIG =  Int32.MaxValue; 
      private const int MSEED = 161803398; 
      private const int MZ = 0;
 

      //
      // Member Variables
      // 
      private int inext, inextp;
      private int[] SeedArray = new int[56]; 
 
      //
      // Public Constants 
      //

      //
      // Native Declarations 
      //
 
      // 
      // Constructors
      // 

      public Random()
        : this(Environment.TickCount) {
      } 

      public Random(int Seed) { 
        int ii; 
        int mj, mk;
 
        //Initialize our Seed array.
        //This algorithm comes from Numerical Recipes in C (2nd Ed.)
        mj = MSEED - Math.Abs(Seed);
        SeedArray[55]=mj; 
        mk=1;
        for (int i=1; i<55; i++) {  //Apparently the range [1..55] is special (Knuth) and so we're wasting the 0'th position. 
          ii = (21*i)%55; 
          SeedArray[ii]=mk;
          mk = mj - mk; 
          if (mk<0) mk+=MBIG;
          mj=SeedArray[ii];
        }
        for (int k=1; k<5; k++) { 
          for (int i=1; i<56; i++) {
        SeedArray[i] -= SeedArray[1+(i+30)%55]; 
        if (SeedArray[i]<0) SeedArray[i]+=MBIG; 
          }
        } 
        inext=0;
        inextp = 21;
        Seed = 1;
      } 

      // 
      // Package Private Methods 
      //
 
      /*====================================Sample====================================
      **Action: Return a new random number [0..1) and reSeed the Seed array.
      **Returns: A double [0..1)
      **Arguments: None 
      **Exceptions: None
      ==============================================================================*/ 
      protected virtual double Sample() { 
          //Including this division at the end gives us significantly improved
          //random number distribution. 
          return (InternalSample()*(1.0/MBIG));
      }

      private int InternalSample() { 
          int retVal;
          int locINext = inext; 
          int locINextp = inextp; 

          if (++locINext >=56) locINext=1; 
          if (++locINextp>= 56) locINextp = 1;

          retVal = SeedArray[locINext]-SeedArray[locINextp];
 
          if (retVal<0) retVal+=MBIG;
 
          SeedArray[locINext]=retVal; 

          inext = locINext; 
          inextp = locINextp;

          return retVal;
      } 

      // 
      // Public Instance Methods 
      //
 

      /*=====================================Next=====================================
      **Returns: An int [0..Int32.MaxValue)
      **Arguments: None 
      **Exceptions: None.
      ==============================================================================*/ 
      public virtual int Next() { 
        return InternalSample();
      } 

      private double GetSampleForLargeRange() {
          // The distribution of double value returned by Sample
          // is not distributed well enough for a large range. 
          // If we use Sample for a range [Int32.MinValue..Int32.MaxValue)
          // We will end up getting even numbers only. 
 
          int result = InternalSample();
          // Note we can't use addition here. The distribution will be bad if we do that. 
          bool negative = (InternalSample()%2 == 0) ? true : false;  // decide the sign based on second sample
          if( negative) {
              result = -result;
          } 
          double d = result;
          d += (Int32.MaxValue - 1); // get a number in range [0 .. 2 * Int32MaxValue - 1) 
          d /= 2*(uint)Int32.MaxValue - 1  ; 
          return d;
      } 


      /*=====================================Next=====================================
      **Returns: An int [minvalue..maxvalue) 
      **Arguments: minValue -- the least legal value for the Random number.
      **           maxValue -- One greater than the greatest legal return value. 
      **Exceptions: None. 
      ==============================================================================*/
      public virtual int Next(int minValue, int maxValue) { 
          if (minValue>maxValue) {
              throw new ArgumentOutOfRangeException("minValue",String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("Argument_MinMaxValue"), "minValue", "maxValue"));
          }
 
          long range = (long)maxValue-minValue;
          if( range <= (long)Int32.MaxValue) { 
              return ((int)(Sample() * range) + minValue); 
          }
          else { 
              return (int)((long)(GetSampleForLargeRange() * range) + minValue);
          }
      }
 

      /*=====================================Next===================================== 
      **Returns: An int [0..maxValue) 
      **Arguments: maxValue -- One more than the greatest legal return value.
      **Exceptions: None. 
      ==============================================================================*/
      public virtual int Next(int maxValue) {
          if (maxValue<0) {
              throw new ArgumentOutOfRangeException("maxValue", String.Format(CultureInfo.CurrentCulture, Environment.GetResourceString("ArgumentOutOfRange_MustBePositive"), "maxValue")); 
          }
          return (int)(Sample()*maxValue); 
      } 

 
      /*=====================================Next=====================================
      **Returns: A double [0..1)
      **Arguments: None
      **Exceptions: None 
      ==============================================================================*/
      public virtual double NextDouble() { 
        return Sample(); 
      }
 

      /*==================================NextBytes===================================
      **Action:  Fills the byte array with random bytes [0..0x7f].  The entire array is filled.
      **Returns:Void 
      **Arugments:  buffer -- the array to be filled.
      **Exceptions: None 
      ==============================================================================*/ 
      public virtual void NextBytes(byte [] buffer){
        if (buffer==null) throw new ArgumentNullException("buffer"); 
        for (int i=0; i<buffer.Length; i++) {
          buffer[i]=(byte)(InternalSample()%(Byte.MaxValue+1));
        }
      } 
    }
 
 

}