title: Convert expression in string to a value
body: <p>I have a string with following statement:</p>
  <pre><code>$expr = &quot;20 * 10 + 5&quot;;
  echo $expr; 
  </code></pre>
  <p>If I print the above string, then it shows me following output:</p>
  <pre><code>20 * 10 + 5
  </code></pre>
  <p>If I do as <code>echo (float)$expr</code>
  then it shows wrong output as <code>20</code></p>
  <p>I want full calculated value as <code>205</code></p>