title: fill a 2 dimentional vector
body: <p>I have a set of primary vectors now I want to push them back into a 2dim vector, but I am not completely sure how can I assign each primary vector to a 1dimention of 2D vector?</p>
  
  <pre><code>vector&lt; vector&lt;int&gt;&gt; V;
   vector&lt;int&gt; p1; 
  vector&lt;int&gt; p2;
  vector&lt;int&gt; p3;
  P1=[0,1,2,3];
  p2=[4,5,6,7];
  p3=[8,9,10,11];
  </code></pre>
  
  <p>What I want is to fill V as below:</p>
  
  <pre><code>V={{0,1,2,3},{4,5,6,7},{8,9,10,11}};
  </code></pre>
  
  <p>Can I do it as below::</p>
  
  <pre><code>V.push_back(p1);
  V.push_back(p2);
  V.push_back(p3);
  </code></pre>