CppMultiply.md

 

 

 

 

 

(C++) Multiply

 

Multiply is a math code snippet to multiply each element in a std::vector by a certain value.

 

Multiply can be defined in multiple ways:

1. Multiply using an algorithm and the C++11 STL
2. Using an algorithm and the STL
3. Using an algorithm and Boost
4. Using a for loop

 

• Download the Qt Creator project 'CppMultiply' (zip)

 

Prefer algorithms over loops [1][2].

 

 

 

 

 

Multiply using an algorithm and the C++11 STL

 

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#include <algorithm> #include <vector> void Multiply(std::vector<int>& v, const int x) {   std::for_each(v.begin(),v.end(),     [x](int& i) { i*=x; } ); }

 

 

 

 

 

Multiply using an algorithm and the STL

 

This is the answer of Exercise #9: No for-loops.

 

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#include <algorithm> #include <functional> #include <numeric> #include <vector>   void Multiply(std::vector<int>& v, const int x) {   std::transform(v.begin(),v.end(),v.begin(),     std::bind2nd(std::multiplies<int>(),x)); }

 

 

 

 

 

Multiply using an algorithm and Boost

 

This is the answer of Exercise #9: No for-loops.

 

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#include <algorithm> #include <functional> #include <numeric> #include <vector> #include <boost/bind.hpp>   void Multiply(std::vector<int>& v, const int x) {   std::transform(v.begin(),v.end(),v.begin(),     boost::bind(std::multiplies<int>(),_1,x)); }

 

 

 

 

 

Multiply using a for loop

 

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#include <vector>   void Multiply(std::vector<int>& v, const int x) {   const int sz = v.size();   for (int i=0; i!=sz; ++i)   {     v[i]*=x;   } }

 

Prefer algorithms over loops [1][2].

 

 

 

 

 

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'