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##### cpp_rational

`#include <boost/multiprecision/cpp_int.hpp>`

    namespace boost{ namespace multiprecision{

    typedef rational_adaptor<cpp_int_backend<> >    cpp_rational_backend;

    typedef number<cpp_rational_backend>         cpp_rational;

    }} // namespaces

The `cpp_rational_backend` type is used via the typedef `boost::multiprecision::cpp_rational`. It provides a rational number type that is a drop-in replacement for the native C++ number types, but with unlimited precision.

As well as the usual conversions from arithmetic and string types, instances of `cpp_rational` are copy constructible and assignable from type `cpp_int`.

There is also a two argument constructor that accepts a numerator and denominator: both of type `cpp_int`.

There are also non-member functions:

    cpp_int numerator(const cpp_rational&);
    cpp_int denominator(const cpp_rational&);

which return the numerator and denominator of the number.

Things you should know when using this type:

- Default constructed `cpp_rational`s have the value zero.
- Division by zero results in a `std::overflow_error` being thrown.
- Conversion from a string results in a `std::runtime_error` being thrown if the string can not be interpreted as a valid rational number.

###### Example:

    #include <boost/multiprecision/cpp_int.hpp>
    #include <iostream>

    int main()
    {
       using namespace boost::multiprecision;

       cpp_rational v = 1;

       // Do some arithmetic:
       for(unsigned i = 1; i <= 1000; ++i)
          v *= i;
       v /= 10;

       std::cout << v << std::endl; // prints 1000! / 10
       std::cout << numerator(v) << std::endl;
       std::cout << denominator(v) << std::endl;

       cpp_rational w(2, 3);  // component wise constructor
       std::cout << w << std::endl; // prints 2/3
       return 0;
    }