title: How to create a vector of vectors?
body: <p>I have this code so far:
      #include "std_lib_facilities_4.h"</p>
  
  <pre><code>void numbers()
  {
      vector&lt;int&gt; first;
      vector&lt;int&gt; second;
      vector&lt;int&gt; third;
      vector&lt;int&gt; fourth;
      vector&lt; &lt;vector&lt;data&gt; &gt; all;
      for (int i = 0; i &lt;= 9; ++i)
      {
              first.push_back(i);
              second.push_back(i);
              third.push_back(i);
              fourth.push_back(i);
      }
      all.push_back(first);
      all.push_back(second);
      all.push_back(third);
      all.push_back(fourth);
      cout &lt;&lt; all[0] &lt;&lt; '\n';
      cout &lt;&lt; all[1] &lt;&lt; '\n';
      cout &lt;&lt; all[2] &lt;&lt; '\n';
      cout &lt;&lt; all[3] &lt;&lt; '\n';
  
  }
  
  int main()
  {
      numbers();
  }
  </code></pre>
  
  <p>How do I create a vector 'all' made up of the vectors 'first', 'second', 'third', and 'fourth'?</p>