title: What is the meaning of associative array?
body: <p>I'm reading The C++ Standard Library: A Tutorial and Reference book. In map example:</p>
  
  <pre><code>   typedef map&lt;string,float&gt; StringFloatMap;
     StringFloatMap coll;
  
     //insert some elements into the collection
     coll["VAT"] = 0.15;
     coll["Pi"] = 3.1415;
     coll["an arbitrary number"] = 4983.223;
     coll["Null"] = 0;
  </code></pre>
  
  <p>The author say:</p>
  
  <blockquote>
    <p>Here, the index is used as the key and may have any type. This is the interface of an associative array. An associative array is an array in which the index may be of an <strong>arbitrary type</strong>.</p>
  </blockquote>
  
  <p>Any one could explain me, what <strong>arbitrary type</strong> means in associative array?</p>