title: double() function in c++ or not?
body: <p>I hava following C++ code</p>
  
  <pre><code>#include &lt;cstdlib&gt;
  #include &lt;iostream&gt;
  #include &lt;fstream&gt;
  #include &lt;time.h&gt;
  #include &lt;math.h&gt;
  
  using namespace std;
  
  #define pi 3.1415926
  
  int n;
  double* a,*b;
  double Function(double);
  
  double A(int j)
  {
      double S=0;
      int ii;
      for (int i=-n;i&lt;n+1;i++)
      {
          S=S+Function(2*pi*double(i)/(2*n+1))*cos(2*pi*double(j)*double(i)/(2*n+1));
      }
      if (j==0)
          return 1/double(2*n+1)*S;
      return 2/double(2*n+1)*S;
  }
  </code></pre>
  
  <p>and  there isn't any declared function <code>double()</code>, and I looked for this function in math.h library and haven't found such. Can you explain what is it, is it a lambda expression or some delegate ? </p>