Generate random number belonging to exponential distribution [duplicate]

This question already has an answer here:

• Why do I always get the same sequence of random numbers with rand()? 12 answers

I'm trying to generate random values belonging to an exponential distribution.

#include <stdio.h>
#include <stdlib.h>
#include <stdint.h>
#include <iostream>
#include <math.h>


using namespace std;

int main(){


    double x;
    double random;
    double one=1.0;
    for(int i=0; i<1000; i++){
        x = ((double) rand() / (RAND_MAX));
        cout << random <<endl;
        x=log(one-random)/(-3);
        cout<< x<< endl;
        cout<< "__"<<endl;

    }



    return 0;
}

I'm using this formula x = log(1-u)/(−λ) that I have read in this post Pseudorandom Number Generator - Exponential Distribution

but the output that I see is this one:

3.90272e-319
0
__
3.90272e-319
0
__
3.90272e-319
0
__
3.90272e-319
0
__
and so on

it is always printed the same value of the random number and also the result of the logarithm is always 0, I can't understand way.