# (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

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

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

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

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

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

Prefer algorithms over loops [1,2].

 ``` #include //From http://www.richelbilderbeek.nl/CppReciprocal.htm void Reciprocal(std::vector& 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.'