 <blockquote> <p>I know these kind of insertions (and their differences):</p> <pre><code>Map[key] = value; </code></pre> </blockquote> <p><code>Map[key]</code> is not strictly for insertions. You can assign to that value as well. The postincr/postdecr operators do modify those values, as a side effect.</p> <p>So <code>Map[key]++</code> is legal, and does what you might expect -- increments the value stored at <code>Map[key]</code>. Equivalent to:</p> <pre><code>Map[key] = Map[key] + 1 </code></pre>