std::geometric_distribution(3)

NAME
std::geometric_distribution - std::geometric_distribution

Synopsis
   Defined in header <random>
   template< class IntType = int > (since C++11)
   class geometric_distribution;
   Produces random non-negative integer values i, distributed according to discrete
   probability function:
   \(P(i|p) = p \cdot (1-p)^i\)P(i|p) = p · (1 − p)i
   The value represents the number of failures in a series of independent yes/no trials
   (each succeeds with probability p), before exactly 1 success occurs.
   std::geometric_distribution<>(p) is exactly equivalent to
   std::negative_binomial_distribution<>(1, p). It is also the discrete counterpart of
   std::exponential_distribution.
   std::geometric_distribution satisfies RandomNumberDistribution.

Template parameters
             The result type generated by the generator. The effect is undefined if
   IntType - this is not one of short, int, long, long long, unsigned short, unsigned
             int, unsigned long, or unsigned long long.

Member types
   Member type Definition
   result_type (C++11) IntType
   param_type (C++11) the type of the parameter set, see RandomNumberDistribution.

Member functions
   constructor constructs new distribution
   (C++11) (public member function)
   reset resets the internal state of the distribution
   (C++11) (public member function)

Generation
   operator() generates the next random number in the distribution
   (C++11) (public member function)

Characteristics
   p returns the p distribution parameter (probability of a trial
   (C++11) generating true)
                 (public member function)
   param gets or sets the distribution parameter object
   (C++11) (public member function)
   min returns the minimum potentially generated value
   (C++11) (public member function)
   max returns the maximum potentially generated value
   (C++11) (public member function)

Non-member functions
   operator==
   operator!= compares two distribution objects
   (C++11) (function)
   (C++11)(removed in C++20)
   operator<< performs stream input and output on pseudo-random number
   operator>> distribution
   (C++11) (function template)

Example
   std::geometric_distribution<>(0.5) is the default and represents the number of coin
   tosses that are required to get heads. // Run this code
 #include <iomanip>
 #include <iostream>
 #include <map>
 #include <random>
 #include <string>
 int main()
 {
     std::random_device rd;
     std::mt19937 gen(rd());
     std::geometric_distribution<> d;
         // same as
         // std::negative_binomial_distribution<> d(1, 0.5):
     std::map<int, int> hist;
     for (int n = 0; n != 10000; ++n)
         ++hist[d(gen)];
     for (auto [x, y] : hist)
     {
         const char c = x < 10 ? x + '0' : x - 10 + 'a';
         std::cout << c << ' ' << std::string(y / 100, '*') << '\n';
     }
 }

Possible output:
 0 *************************************************
 1 *************************
 2 ************
 3 ******
 4 **
 5 *
 6
 7
 8
 9

External links
   Weisstein, Eric W. "Geometric Distribution." From MathWorld — A Wolfram Web
   Resource.