How to generate random float number in C

Question

I can t find any solution to generate a random float number in the range of  0 a   where a is some float defined by a user   I have tried the following  but it doesn t seem to work correctly   float x  float rand     float RAND MAX a

User · Accepted Answer

Try   float x    float rand    float  RAND MAX a     To understand how this works consider the following    N   a random value in  0  RAND MAX  inclusively    The above equation  removing the casts for clarity  becomes   N  RAND MAX a    But division by a fraction is the equivalent to multiplying by said fraction s reciprocal  so this is equivalent to   N    a RAND MAX    which can be rewritten as   a    N RAND MAX    Considering N RAND MAX is always a floating point value between 0 0 and 1 0  this will generate a value between 0 0 and a   Alternatively  you can use the following  which effectively does the breakdown I showed above  I actually prefer this simply because it is clearer what is actually going on  to me  anyway    float x     float rand    float  RAND MAX     a    Note  the floating point representation of a must be exact or this will never hit your absolute edge case of a  it will get close   See this article for the gritty details about why   Sample   include  lt stdio h gt   include  lt stdlib h gt   include  lt time h gt   int main int argc  char  argv          srand  unsigned int time NULL         float a   5 0      for  int i 0 i lt 20 i            printf   f n     float rand    float  RAND MAX     a       return 0      Output  1 625741 3 832026 4 853078 0 687247 0 568085 2 810053 3 561830 3 674827 2 814782 3 047727 3 154944 0 141873 4 464814 0 124696 0 766487 2 349450 2 201889 2 148071 2 624953 2 578719

User · Answer

If you want to generate a random float in a range  try a next solution    include  lt stdio h gt   include  lt stdlib h gt   include  lt time h gt    float random float const float min  const float max        if  max    min  return min      else if  min  lt  max  return  max - min      float rand     RAND MAX    min          return 0 if min  gt  max     return 0      int main  const int argc  const char  argv          srand time NULL         char line      -------------------------------------------        float data 10  2               -10  10            -5   5            -1  1            -0 25  -0 15            1 5  1 52            -1700  8000            -0 1  0 1            -1  0            -1  -2            1 2  1 1              puts line       puts       From         Result           To        puts line         int i      for  i   0  i  lt  10    i            printf   12f    12f    12f n   data i  0   random float data i  0   data i  1    data i  1               puts line        return 0      A result  values is fickle   -------------------------------------------      From         Result           To -------------------------------------------   -10 000000       2 330828      10 000000    -5 000000      -4 945523       5 000000    -1 000000       0 004242       1 000000    -0 250000      -0 203197      -0 150000     1 500000       1 513431       1 520000 -1700 000000    3292 941895    8000 000000    -0 100000      -0 021541       0 100000    -1 000000      -0 148299       0 000000    -1 000000       0 000000      -2 000000     1 200000       0 000000       1 100000 -------------------------------------------

User · Answer

You can also generate in a range  min  max  with something like  float float rand  float min  float max         float scale   rand      float  RAND MAX      0  1 0         return min   scale     max - min             min  max

User · Answer

while it might not matter now here is a function which generate a float between 2 values   include  lt math h gt   float func Uniform float left  float right        float randomNumber   sin rand     rand         return left    right - left    fabs randomNumber

User · Answer

This generates a random float between two floats  float RandomFloat float min  float max      return   max - min      float rand     RAND MAX     min

[c] How to generate random float number in C

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