Sort or Mergesort based on user input
<p>I am trying to call a function based on user input. I cannt figure out what I am doing wrong. I keep getting this error</p>

<pre><code>error: no matching function for call to 'sort(std::vector&lt;int, std::allocator&lt;int&gt; &gt;&amp;)'
</code></pre>

<p>Can someone tell me what I am doing wrong. Please explain any suggestions thoroughly as I am brand new to C++. Here is my code:</p>

<pre><code>#include &lt;iterator&gt;
#include &lt;algorithm&gt;
#include &lt;vector&gt;
#include &lt;fstream&gt;
#include &lt;iostream&gt;
#include &lt;string&gt;

std::ifstream in("");
std::ofstream out("outputfile.txt");
std::vector&lt;int&gt; numbers;
std::string sortType = "";
std::string file = "";

int main()
{
  std::cout &lt;&lt; "Which type of sort would you like to perform(sort or mergesort)?\n";
  std::cin &gt;&gt; sortType;

  std::cout &lt;&lt; "Which file would you like to sort?\n";
  std::cin &gt;&gt; file;

  //Check if file exists
  if(!in)
  {
    std::cout &lt;&lt; std::endl &lt;&lt; "The File is corrupt or does not exist! ";
    return 1;
  }

  // Read all the ints from in:
  copy(std::istream_iterator&lt;int&gt;(in), std::istream_iterator&lt;int&gt;(),
            std::back_inserter(numbers));

  //check if the file has values
  if(numbers.empty())
  {
      std::cout &lt;&lt; std::endl &lt;&lt; "The file provided is empty!";
      return 1;
  } else
  {
      if(file == "sort")
      {
          sort(numbers);
      }else
      {
          mergeSort();
      }
  }
}

void sort(std::vector&lt;int&gt;)
{

  // Sort the vector:
  sort(numbers.begin(), numbers.end());

  unique(numbers.begin(), numbers.end());

  // Print the vector with tab separators:
  copy(numbers.begin(), numbers.end(),
            std::ostream_iterator&lt;int&gt;(std::cout, "\t"));
  std::cout &lt;&lt; std::endl;

    // Write the vector to a text file
  copy(numbers.begin(), numbers.end(),
            std::ostream_iterator&lt;int&gt;(out, "\t"));
    std::cout &lt;&lt; std::endl;
}

void mergeSort()
{
      //mergesort code..
}
</code></pre>
