generate random double numbers in c++

Here's how

double fRand(double fMin, double fMax)
{
    double f = (double)rand() / RAND_MAX;
    return fMin + f * (fMax - fMin);
}

Remember to call srand() with a proper seed each time your program starts.

[Edit] This answer is obsolete since C++ got it's native non-C based random library (see Alessandro Jacopsons answer) But, this still applies to C

This solution requires C++11 (or TR1).

#include <random>

int main()
{
   double lower_bound = 0;
   double upper_bound = 10000;
   std::uniform_real_distribution<double> unif(lower_bound,upper_bound);
   std::default_random_engine re;
   double a_random_double = unif(re);

   return 0;
}

For more details see John D. Cook's "Random number generation using C++ TR1".

See also Stroustrup's "Random number generation".