How to change the value of text feilds after the button is clicked

[nehaquick]

I have a form where the user has to enter values. to make it easy for the user there are some values already present in the feilds but if the user wants he can change it. the problem is i want to have a button which upon clicking should enter the value "null" to the feild. one of the text feild code i m displaying here

<input name="departFrom" type="text" id="departFrom" <?php 
      if ($_POST['Void']=='Void') {
      echo "NULL"; 
      exit();
      } else  {
      echo $row_query2['arrivalTo'];
      }
      ?>/>
 

[Please use CODE tags when posting source code. Thanks! --pbmods]

the button is
<input name="Void" type="button" id="Void" value="Void"/>

i didn't put the type as submit as the button is not submitting the form just changing the values. the problem here is its not acknowledging the if condition. I think the condition for checking the button is not right. i tried with if (isset($_POST['Void'])) as well but still its not working.
please can u guide me.

thanks in advance

[epots9]

u forgot value

[HTML]<input name="departFro m" type="text" id="departFrom " value="<?php
if ($_POST['Void']=='Void') {
echo 'NULL';
} else {
echo $row_query2['arrivalTo'];
}
?>" />
[/HTML]

does that work?

[ronnil]

for that kind of behaviour you need javascript, this can be implemented rather simply:

<input type="text" name="somename" onfocus="this.value='null'" value="standardvalue">

[Please use CODE tags when posting source code. Thanks! --pbmods]

now when the textfield gains focus, the textfields value is set to 'null'. (you might just wanna put an empty string in there or just select the whole text instead)

[nehaquick]

Thanks for the reply. I had tried that as well. Its still not working. My problem is how to check the button is clicked or not. once the condition is set then it will automatically assign the value.