title: stopping fibonacci input negatiive
body: <p>so i have made a fibonacci cycle but i need to make it stop when it hits a certain number and it must get higher than that. That part is not the problem mine problem is that i made a html where you can input the number but when you put in a negative number it doesnt do anything can someone help me
  here is mine code </p>
  
  <pre><code>$a=0;
  $b=1;
  $c=$_POST["fibi"];
  
  
  
  
      for ($i = 0; $i &lt;= $c; $i++) {
  
          $z = $a + $b;
          echo $z."&lt;br /&gt;";
  
          if ($c == 0){
  
              echo 'the highest number is 0';
              break;
  
              }elseif($c &lt; 0){
  
                  echo "please enter a positive number";
                  break;
          }
              elseif($z &gt;= $c){
  
                  echo "the highest number is $latest";
                  break;
              }
  
  
          $latest = $z;
          $a = $b;
          $b = $z;
  
              }
  
      &lt;!DOCTYPE html&gt;
  
          &lt;html lang="en"&gt;
          &lt;head&gt;
              &lt;meta charset="UTF-8"&gt;
              &lt;title&gt;fibi&lt;/title&gt;
          &lt;/head&gt;
          &lt;body&gt;
          &lt;form action="fibi.php" method="post"&gt;
              input:&lt;input type= "number" name="fibi"&gt; &lt;/form&gt;&lt;br&gt;
          &lt;/body&gt;
          &lt;/html&gt;
  </code></pre>