How to generate random float number in C -

possible duplicate:
c++ random float
how generate random number in c?

i can't find solution find random float number [0,a], a float defined user.

i have tried following, doesn't seem work correctly.

float x=(float)rand()/((float)rand_max/a) 

try:

float x = (float)rand()/(float)(rand_max/a); 

to understand how works consider following.

n = random value in [0..rand_max] inclusively. 

the above equation (removing casts clarity) becomes:

n/(rand_max/a) 

but division fraction equivalent multiplying said fraction's reciprocal, equivalent to:

n * (a/rand_max) 

which can rewritten as:

a * (n/rand_max) 

considering n/rand_max floating point value between 0.0 , 1.0, generate value between 0.0 , a.

alternatively, can use following, breakdown showed above. prefer because clearer going on (to me, anyway):

float x = ((float)rand()/(float)(rand_max)) * a; 

note: floating point representation of a must exact or never hit absolute edge case of a (it close). see this article gritty details why.

sample

#include <stdio.h> #include <stdlib.h> #include <time.h>  int main(int argc, char *argv[]) {     srand((unsigned int)time(null));      float = 5.0;     (int i=0;i<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