[algorithm] C++ for_each

1. Traditonal for()

for (int i = 0; i < 10; i++)
{
  std::cout << i << std::endl;
}

Commonly used for function in C++.
We declare integer and iterate this integer.

2. for() additional in C++11

for (int i : {0, 1, 2, 3, 4, 5})
{
  std::cout << i << std::endl;
}

std::vector<std::string> name_vector;
for (const auto& element : name_vector)
{
  std::cout << element << std::endl;
}

We called Range-based for loop.
Used Iterator internally, executing all elements in container like vector.
Looking neat is the biggest advantage.
Performance is same as traditinal for.

3. std::for_each()

#include <algorithm>
std::vector<std::string> name_vector{ "test1", "test2", "test3" };
std::for_each(name_vector.begin(), name_vector.end(), [](auto& input) {std::cout << input << std::endl; });

#include <algorithm>
void print(std::string& input)
{
  std::cout << input << std::endl;
}
std::vector<std::string> name_vector{ "test1", "test2", "test3" };
std::for_each(name_vector.begin(), name_vector.end(), print);

for_each is defined at algorithm header.
So you should wirte std::for_each form.
received parameter is start iterator, end iterator, function.
Last parameter can use lamda form.

4. std::transform()

#include <algorithm>
std::string change(std::string& input)
{
  return std::string("Changed!");
}
std::vector<std::string> name_vector{ "test1", "test2", "test3" };
std::vector<std::string> result{ "result1", "result2", "result3" };  
std::transform(name_vector.begin(), name_vector.end(), result.begin(), change);
//result = {"Changed!", "Changed!", "Changed!"}

transform also used iterator.
Stored result to another container.
Of course, stored in original container.
Last parameter can use lamda form.

TODO: std::for_each-n(C++17)