Getting the same random double number at each run in C++ [duplicate]

I need to generate uniformly distributed random numbers for a Monte Carlo simulation. I read this thread Random double C++11 and followed the suggestions but, still, I am getting the same number whenever I run the program in Code Blocks. Here is my code:

#include <iostream>  
#include <random>    

int main(){

    std::random_device rd;                              // use random_device to get a random seed
    std::mt19937 mt(rd());                              // mt19937 is a proper pseudo-random number generator 
    std::uniform_real_distribution<double> unif(0,1);   // generate uniformly distributed random doubles in [0,1]

    double x = unif(mt);
    std::cout << x << std::endl;
}

Any suggestion why that happens?