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    copied!<p>I'd take advantage of <a href="http://php.net/manual/en/function.is-numeric.php" rel="nofollow">is_numeric</a> and also test for 0 before dividing like so:</p> <pre><code>&lt;?php $valuea=''; $valueb=''; $valuec=''; $answer=''; if (isset($_POST['valuea'])) $valuea = $_POST['valuea']; if (isset($_POST['valueb'])) $valueb = $_POST['valueb']; if (isset($_POST['valuec'])) $valuec = $_POST['valuec']; if(is_numeric($valuea) &amp;&amp; is_numeric($valueb) &amp;&amp; is_numeric($valuec)) { if($valuec=='0') { $answer ="Error: Dividing by zero"; } else{ $answer = ($valuea - $valueb) / $valuec; } } echo &lt;&lt;&lt;_END &lt;form method='post'&gt; &lt;table border='0' width='500px' cellpadding='3' cellspacing='1' class="table"&gt; &lt;tr class="calcheading"&gt;&lt;td colspan="2"&gt;&lt;strong&gt;Stright Line Depreciation&lt;/strong&gt;&lt;/td&gt;&lt;/tr&gt; &lt;tr class="calcrow"&gt;&lt;td&gt;Enter Cost:&lt;/td&gt;&lt;td align="center"&gt;&lt;input type="text" name="valuea" value="$valuea" /&gt;&lt;/td&gt;&lt;/tr&gt; &lt;tr class="calcrow2"&gt;&lt;td&gt;End Salvage Value:&lt;/td&gt;&lt;td align="center"&gt;&lt;input type="text" name="valueb" value="$valueb" /&gt;&lt;/td&gt;&lt;/tr&gt; &lt;tr class="calcrow"&gt;&lt;td&gt;Enter Estimated Life:&lt;/td&gt;&lt;td align="center"&gt;&lt;input type="text" name="valuec" value="$valuec" /&gt;&lt;/td&gt;&lt;/tr&gt; &lt;tr class="submit"&gt;&lt;td colspan="2"&gt;&lt;input type="submit" value="Calculate" /&gt;&lt;/td&gt;&lt;/tr&gt; _END; ?&gt; &lt;tr class="calcrow"&gt;&lt;td&gt;&lt;em&gt;The answer is:&lt;/em&gt;&lt;/td&gt;&lt;td align="center"&gt;&lt;input type="text" value="&lt;?php echo is_numeric($answer)?round($answer):$answer; ?&gt;"&gt;&lt;/td&gt;&lt;/tr&gt; &lt;/table&gt; &lt;/form&gt; </code></pre> <p>Here's a <a href="http://phpfiddle.org/main/code/f2u-cir" rel="nofollow">phpfiddle</a> and <a href="http://phpfiddle.org/api/run/f2u-cir" rel="nofollow">its results</a>.</p>
 

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