# std::bernoulli_distribution

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< cpp‎ | numeric‎ | random

Defined in header `<random>` |  |
class bernoulli_distribution; |  | (since C++11)

Produces random boolean values, according to the discrete probability function. The probability of true is

  P(b|p) =⎧
  ⎨
  ⎩p if b == true
  1 − p if b == false

`std::bernoulli_distribution` satisfies `RandomNumberDistribution`

### Member types

Member type | Definition
`result_type` | bool
`param_type` | the type of the parameter set, see `RandomNumberDistribution`.

### Member functions

(constructor) | constructs new distribution (public member function)
reset | resets the internal state of the distribution (public member function)

##### Generation

operator() | generates the next random number in the distribution (public member function)

##### Characteristics

p | returns the p distribution parameter (probability of generating true) (public member function)
param | gets or sets the distribution parameter object (public member function)
min | returns the minimum potentially generated value (public member function)
max | returns the maximum potentially generated value (public member function)

### Non-member functions

operator==operator!= | compares two distribution objects (function)
operator<<operator>> | performs stream input and output on pseudo-random number distribution (function template)

### Example

Run this code

    #include <iostream>
    #include <iomanip>
    #include <string>
    #include <map>
    #include <random>

    int main()
    {
        std::random_device rd;
        std::mt19937 gen(rd());
        // give "true" 1/4 of the time
        // give "false" 3/4 of the time
        std::bernoulli_distribution d(0.25);

        std::map<bool, int> hist;
        for(int n=0; n<10000; ++n) {
            ++hist[d(gen)];
        }
        for(auto p : hist) {
            std::cout << std::boolalpha << std::setw(5) << p.first
                      << ' ' << std::string(p.second/500, '*') << '\n';
        }
    }

Possible output:

    false ***************
     true ****

### External links

Weisstein, Eric W. "Bernoulli Distribution." From MathWorld--A Wolfram Web Resource.

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