How to generate a random number between 0 and 1

Question

I want to generate random numbers between  0 1   I am trying the following   double r2         return  rand     10000    10000 0      int SA         double u      u   r2        But it doesn t generate the expected result  How can I fix it

User · Answer

Here s a general procedure for producing a random number in a specified range   int randInRange int min  int max      return min    int   rand      double   RAND MAX   1     max - min   1        Depending on the PRNG algorithm being used  the   operator may result in a very non-random sequence of numbers

User · Answer

In your version rand     10000 will yield an integer between 0 and 9999   Since RAND MAX may be as little as 32767  and since this is not exactly divisible by 10000 and not large relative to 10000  there will be significant bias in the  randomness  of the result  moreover  the maximum value will be 0 9999  not 1 0  and you have unnecessarily restricted your values to four decimal places   It is simple arithmetic  a random number divided by the maximum possible random number will yield a number from 0 to 1 inclusive  while utilising the full resolution and distribution of the RNG  double r2         return  double rand      double RAND MAX       Use  double rand      double   unsigned RAND MAX   1  if exclusion of 1 0 was intentional

User · Answer

Set the seed using srand    Also  you re not specifying the max value in rand    so it s using RAND MAX  I m not sure if it s actually 10000    why not just specify it  Although  we don t know what your  expected results  are  It s a random number generator  What are you expecting  and what are you seeing   As noted in another comment  SA   isn t returning anything explicitly   http   pubs opengroup org onlinepubs 009695399 functions rand html http   www thinkage ca english gcos expl c lib rand html  Edit  From Generating random number between  -1  1  in C    float rand    RAND MAX returns a floating-point number in  0 1

User · Answer

It seems to me you have not called srand first  Usage example here

User · Answer

Have you tried with  replacing   rand     10000    10000 0   with  rand     2   This worked for me   So you could do something like this   double r2          srand time NULL         return rand     2

User · Answer

double r2        return  rand     10001    10000 0

[c] How to generate a random number between 0 and 1?

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