Question

Was working on a project with mingw on windows :

C:\Users\...>g++ -dumpversion
4.5.0

When I compiled the code under g++ v 4.2.4 I was getting a segmentation fault – after couple hours I pinned it down to the line :

double decimal = ((double) rand()) / (RAND_MAX + 1);

For some reason this was giving negative values (and one thing led to another).
What reason ?

Edit : cpp :

#include <iostream>
#include "Random.h"
#include <math.h>

using namespace std;
double Random::exponential(int T) {
    double decimal = ((double) rand()) / (RAND_MAX + 1);
    //  std::cout << "decimal : " << decimal << std::endl;
    return log(1 - decimal)*(-T);
}
//etc

h:

#ifndef RANDOM_H
#define RANDOM_H

#include <cstdlib>
#include <math.h>
class Random {
public:
    static double exponential(int T);
    static int random_int(int min, int max);
    static bool coin(); //50% true 50% false
};

#endif  /* RANDOM_H */

just noticed the double include (of math.h) but this shouldn’t be an issue

Answer 1

In your case, RAND_MAX is the maximum value for the integer type it is stored in, so RAND_MAX + 1 gives you the maximum negative value. Technically this is signed integer overflow which is undefined behaviour so anything can happen.

You need to do, as J-16 pointed out,

double decimal = (double)rand() / ((double)RAND_MAX + 1);