Form submission and retaining information the user has submitted

Hi,

How would I retain the value if a user submits a form and makes an error in the submission. For example, a user fills out his first, last, name but forgets his email address. I don’t want the user to have to fill out his first, last name again.

My question is, I’m having a hard time figuring out the above logic in WP. In the below code if a user submits his name and presses submit and forgets a part of the form his first name won’t be avail. and he has to write it again. In my below code, how do I fix this?

if(trim($_POST['contactName']) === '') {

			$nameError = __('You forgot to enter your name.','language');
			$error_message .= 'Your Name\n';
			$hasError = true;

		} else {

			$name = trim($_POST['contactName']);

		}

<div class="pro_fields">
          <li>
            <label for="contactName">
              <?php _e('Name','language');?>
            </label>
            <br/>
            <?php $contactName = $_POST['contactName'];
					if($contactName != '' && $contactName !='Please enter your name'){
						$contactName = $_POST['contactName'];
					}else{
						$contactName = 'Please enter your name';
					}
				?>
            <input type="text" name="contactName" id="cs_contactName" class="field" value="<?php echo $contactName; ?>" class="requiredField" onblur="if(this.value == '') { this.value = 'Please enter your name'; }"  onfocus="if(this.value == 'Please enter your name') { this.value = ''; }" />
            <?php if($nameError != '') { ?>
            <span class="error">
            <?=$nameError;?>
            </span>
            <?php } ?>
          </li>
        </div>