(C++) Reciprocal

 

Reciprocal is a container code snippet to replace all values in a container by their reciprocal (that is: 1/x) (view the wikipedia page on reciprocal).

 

There are multiple ways to perform Reciprocal:

• The general algorithm way (best)
• The algorithm way on a std::vector<double> (intermediate)
• The for-loop way on a std::vector<double> (worst)

 

 

 

 

 

The general algorithm way

 

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#include <algorithm> #include <numeric> //From http://www.richelbilderbeek.nl/CppReciprocal.htm template <class Container> void Reciprocal(Container& c) {   std::transform(c.begin(),c.end(),c.begin(),     std::bind1st(std::divides<Container::value_type>(),1.0));     }

 

 

 

 

 

The algorithm way on a std::vector<double>

 

This way is used as an answer in Exercise #9: No for-loops.

 

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#include <vector> #include <algorithm> #include <numeric> //From http://www.richelbilderbeek.nl/CppReciprocal.htm void Reciprocal(std::vector<double>& v) {   std::transform(v.begin(),v.end(),v.begin(),     std::bind1st(std::divides<double>(),1.0));     }

 

 

 

 

 

The for-loop way on a std::vector<double>

 

Prefer algorithms over loops [1,2].

 

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#include <vector> //From http://www.richelbilderbeek.nl/CppReciprocal.htm void Reciprocal(std::vector<double>& v) {   const int sz = v.size();   for (int i=0; i!=sz; ++i)   {     v[i]=1.0/v[i];   } }

 

 

 

 

 

References

 

1. Bjarne Stroustrup. The C++ Programming Language (3rd edition). ISBN: 0-201-88954-4. Chapter 18.12.1 : 'Prefer algorithms over loops'
2. Herb Sutter and Andrei Alexandrescu. C++ coding standards: 101 rules, guidelines, and best practices. ISBN: 0-32-111358-6. Chapter 84: 'Prefer algorithm calls to handwritten loops.'