Discrete distribution

[vadkortefa]

Hello,

I am trying to implement the example found here:

http://www.cplusplus.com/reference/random/discrete_distribution/

  // discrete_distribution
#include <iostream>
#include <random>

int main()
{
  const int nrolls = 10000; // number of experiments
  const int nstars = 100;   // maximum number of stars to distribute

  std::default_random_engine generator;
  std::discrete_distribution<int> distribution {2,2,1,1,2,2,1,1,2,2};

  int p[10]={};

  for (int i=0; i<nrolls; ++i) {
    int number = distribution(generator);
    ++p[number];
  }

  std::cout << "a discrete_distribution:" << std::endl;
  for (int i=0; i<10; ++i)
    std::cout << i << ": " << std::string(p[i]*nstars/nrolls,'*') << std::endl;

  return 0;
}

But it does not compile. This is the first error I get for line 11:

error C2601: 'distribution' : local function definitions are illegal

Thank you!

[MiiNiPaa]

Are you sure that your compiler is set to work with C++11 standard?

[JLBorges]

Add #include <string>

And if an old version of the Microsoft compiler is used, try inserting an = in line 11

// std::discrete_distribution<int> distribution {2,2,1,1,2,2,1,1,2,2};
std::discrete_distribution<int> distribution = {2,2,1,1,2,2,1,1,2,2};

[vadkortefa]

Not sure. I am using Visual Studio 2012.

[vadkortefa]

I already had #include <string>, and inserting the "=" still gives an error. Thank you, though!

[MiiNiPaa]

Visual studio 2012 is marked as not supporting initializer lists: https://msdn.microsoft.com/en-us/library/hh567368.aspx

You can store probabilities in container and use iterator constructor:

  const int prob_size = 10;
  int probabilities[prob_size] = {2,2,1,1,2,2,1,1,2,2};
  std::discrete_distribution<int> distribution(probabilities, probabilities + prob_size);

[vadkortefa]

Thank you!

This now gives an error for the third line in your code: error C2661: 'std::discrete_distribution<_Ty>::discrete_distribution' : no overloaded function takes 2 arguments

[MiiNiPaa]

It appears that VS2012 missing iterator constructor as well...
Well, only way to initialize it is to use last consructor and ugly hack (I hope at least lambdas are properly supported):

  std::discrete_distribution<int> distribution(10, 0, 10,
                                               [](double d)
                                               {static const int prob[] = {2,2,1,1,2,2,1,1,2,2};
                                                return prob[static_cast<size_t>(d)];});

EDIT: I suggest to update your compiler too. Either 2015 RC, or 2013 would be fine: http://www.cplusplus.com/forum/lounge/169021/

[vadkortefa]

This worked. Thank you very much!