title: 'for_each_n' is not a member of 'std' in C++17
body: <p>I have small piece of code for <code>std::for_each_n</code> loop. I tried running it on inbuilt <a href="http://coliru.stacked-crooked.com/" rel="nofollow noreferrer">Coliru</a> compiler GCC  C++17 using following command :</p>
  
  <pre><code>g++ -std=c++1z -O2 -Wall -pedantic -pthread main.cpp &amp;&amp; ./a.out
  </code></pre>
  
  <p>But compiler give an error that <strong>" 'for_each_n' is not a member of 'std' ".</strong></p>
  
  <p>My code is bellow which is copied from <a href="http://en.cppreference.com/w/cpp/algorithm/for_each_n" rel="nofollow noreferrer">cppreference</a>.</p>
  
  <pre><code>#include &lt;algorithm&gt;
  #include &lt;iostream&gt;
  #include &lt;vector&gt;
  
  int main()
  {
      std::vector&lt;int&gt; ns{1, 2, 3, 4, 5};
      for (auto n: ns) std::cout &lt;&lt; n &lt;&lt; ", ";
      std::cout &lt;&lt; '\n';
      std::for_each_n(ns.begin(), 3, [](auto&amp; n){ n *= 2; });
      for (auto n: ns) std::cout &lt;&lt; n &lt;&lt; ", ";
      std::cout &lt;&lt; '\n';
  }
  </code></pre>
  
  <p>So, Why I'm getting an error?</p>