Code:
<?php
if ( isset ($_POST['source']) )
{ 
$source=$_POST['source'];
}
else
{ 
$source=0;
}
?>

<form method="post">
<input type="text" name="source" value="<?php echo $source ?>">
<input type="text" name="copy" value="<?php echo $source ?>">
<input type="submit">
</form>
I have the code above,
If I enter "someText" in the input box "source" and click the submit button,
"someText" will be seen the input box "copy".

I like to make it like the following.
If I enter "someText" in the input box "source",
"someText" will be simultaneously seen the input box "copy" without clicking the submit button.