Random number generator only generating one random number

Question

I have the following function     Function to get random number public static int RandomNumber int min  int max        Random random   new Random        return random Next min  max       How I call it   byte   mac   new byte 6   for  int x   0  x  lt  6    x      mac x     byte  Misc RandomNumber  int 0xFFFF   int 0xFFFFFF    256     If I step that loop with the debugger during runtime I get different values  which is what I want   However  if I put a breakpoint two lines below that code  all members of the mac array have equal value   Why does that happen

User · Answer

I would rather use the following class to generate random numbers   byte   random  System Security Cryptography RNGCryptoServiceProvider prov   new System Security Cryptography RNGCryptoServiceProvider    prov GetBytes random

User · Answer

Every time you do new Random   it is initialized using the clock  This means that in a tight loop you get the same value lots of times  You should keep a single Random instance and keep using Next on the same instance     Function to get a random number  private static readonly Random random   new Random     private static readonly object syncLock   new object     public static int RandomNumber int min  int max        lock syncLock       synchronize         return random Next min  max               Edit  see comments   why do we need a lock here   Basically  Next is going to change the internal state of the Random instance  If we do that at the same time from multiple threads  you could argue  we ve just made the outcome even more random   but what we are actually doing is potentially breaking the internal implementation  and we could also start getting the same numbers from different threads  which might be a problem - and might not  The guarantee of what happens internally is the bigger issue  though  since Random does not make any guarantees of thread-safety  Thus there are two valid approaches    Synchronize so that we don t access it at the same time from different threads Use different Random instances per thread   Either can be fine  but mutexing a single instance from multiple callers at the same time is just asking for trouble   The lock achieves the first  and simpler  of these approaches  however  another approach might be    private static readonly ThreadLocal lt Random gt  appRandom        new ThreadLocal lt Random gt       gt  new Random       this is then per-thread  so you don t need to synchronize

User · Answer

My answer from here   Just reiterating the right solution   namespace mySpace       public static class Util               private static rnd   new Random            public static int GetRandom                         return rnd Next                        So you can call   var i   Util GetRandom      all throughout    If you strictly need a true stateless static method to generate random numbers  you can rely on a Guid   public static class Util       public static int GetRandom                 return Guid NewGuid   GetHashCode              It s going to be a wee bit slower  but can be much more random than Random Next  at least from my experience   But not   new Random Guid NewGuid   GetHashCode    Next      The unnecessary object creation is going to make it slower especially under a loop   And never   new Random   Next      Not only it s slower  inside a loop   its randomness is    well not really good according to me

User · Answer

For ease of re-use throughout your application a static class may help   public static class StaticRandom       private static int seed       private static ThreadLocal lt Random gt  threadLocal   new ThreadLocal lt Random gt                gt  new Random Interlocked Increment ref seed          static StaticRandom                 seed   Environment TickCount             public static Random Instance   get   return threadLocal Value          You can use then use static random instance with code such as  StaticRandom Instance Next 1  100

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There are a lot of solutions  here one  if you want only number erase the letters and the method receives a random and the result length   public String GenerateRandom Random oRandom  int iLongitudPin        String sCharacters    123456789ABCDEFGHIJKLMNPQRSTUVWXYZ123456789       int iLength   sCharacters Length      char cCharacter      int iLongitudNuevaCadena   iLongitudPin       String sRandomResult           for  int i   0  i  lt  iLongitudNuevaCadena  i                  cCharacter   sCharacters oRandom Next iLength            sRandomResult    cCharacter ToString              return  sRandomResult

User · Answer

1  As Marc Gravell said  try to use ONE random-generator  It s always cool to add this to the constructor  System Environment TickCount   2  One tip  Let s say you want to create 100 objects and suppose each of them should have its-own random-generator  handy if you calculate LOADS of random numbers in a very short period of time   If you would do this in a loop  generation of 100 objects   you could do this like that  to assure fully-randomness    int inMyRandSeed   for int i 0 i lt 100 i         inMyRandSeed   System Environment TickCount   i                    myNewObject   new MyNewObject inMyRandSeed                          Usage  Random m rndGen   new Random inMyRandSeed     Cheers

User · Answer

I solved the problem by using the Rnd   function  Function RollD6   As UInteger         RollD6    Math Floor 6   Rnd       1         Return RollD6 End Function  When the form loads  I use the Randomize   method to make sure I don t always get the same sequence of random numbers from run to run

User · Answer

Always get a positive random number   var nexnumber   Guid NewGuid   GetHashCode            if  nexnumber  lt  0                        nexnumber    -1

User · Answer

Mark s solution can be quite expensive since it needs to synchronize everytime   We can get around the need for synchronization by using the thread-specific storage pattern    public class RandomNumber   IRandomNumber       private static readonly Random Global   new Random         ThreadStatic  private static Random  local       public int Next int max                var localBuffer    local          if  localBuffer    null                         int seed              lock Global  seed   Global Next                localBuffer   new Random seed                local   localBuffer                    return localBuffer Next max              Measure the two implementations and you should see a significant difference

User · Answer

Every time you execute  Random random   new Random  15     It does not matter if you execute it millions of times  you will always use the same seed   If you use   Random random   new Random       You get different random number sequence  if a hacker guesses the seed and your algorithm is related to the security of your system - your algorithm is broken  I you execute mult  In this constructor the seed is specified by the system clock and if several instances are created in a very short period of time  milliseconds  it is possible that they may have the same seed   If you need safe random numbers you must use the class     System Security Cryptography RNGCryptoServiceProvider   public static int Next int min  int max        if min  gt   max                throw new ArgumentException  Min value is greater or equals than Max value               byte   intBytes   new byte 4       using RNGCryptoServiceProvider rng   new RNGCryptoServiceProvider                  rng GetNonZeroBytes intBytes             return  min    Math Abs BitConverter ToInt32 intBytes  0      max - min   1       Usage   int randomNumber   Next 1 100

[c#] Random number generator only generating one random number

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