changing border in php code

[hwoarang69]

i have a form and inside i have one field and one button. when user hit submit button a php script runs.

in php script i am checking error. ex name is too short etc..

now i want to add a red border only if there is a error. if i get to echo"Error - first name..." than i want to set that input field border red. i am not sure how can i do this. any ideas?

index.php

<?php 
    if(isset($_POST['button'])) 
     {
         //check errors
        if((strlen($_POST['f_input']) < 2))
        {
            echo "Error - first name is too short!";
        }
        else
        {
           ....
        }
     }
?>

<form action='index.php' method='POST'>
  <input type='field' placeholder='first name'  id='f_field' name='f_input'  />
  ...
   <button type="submit" id='button' name="button" >submit</button>
</form>

[TonyG_cyprus]

Use css,

if(strlen($_POST['f_input'])<2))
{
   echo"<input type='text' class='abc' value='<?php $_POST['f_input'] ?>'>";
   }elseif(strlen($_POST['f_input']>2)){

    echo"<input type='text' class='def' value='<?php $_POST['f_input'] ?>'>";
    }

so your css would be like

.abc{
border-color:red;
}
.def{
border-color:black;
}

[hwoarang69]

ah thanks