question about select tag in php

["Sudhakar" <finals27@xxxxxxxxx>]

i have two select tags as part of a registration form, city1 city2 
where city1 has a list of regions and similar for city2

there are different regions for city1 and city2 so instead of all 
the regions appearing one after the other i would like to create a 
blank option followed by the next set of regions for formatting 
purpose only.

ex= 
<select name="city1"> 
<option <?php if ($city1=="region1"){echo "SELECTED";}?> 
value="region1">Select region1</option>
<option <?php if ($city1=="nameofregion1"){echo "SELECTED";}?> 
value="nameofregion1">nameofregion1</option>
<option <?php if ($northisland=="0"){echo "SELECTED";}?> 
value="0"></option>
<option <?php if ($city1=="nameofregion2"){echo "SELECTED";}?> 
value="nameofregion2">nameofregion2</option>
<option <?php if ($northisland=="1"){echo "SELECTED";}?> 
value="1"></option>
</select>


<select name="city2"> 
<option <?php if ($city2=="region2"){echo "SELECTED";}?> 
value="region2">Select region2</option>
<option <?php if ($city2=="nameofregion1"){echo "SELECTED";}?> 
value="nameofregion1">nameofregion1</option>
<option <?php if ($northisland=="2"){echo "SELECTED";}?> 
value="2"></option>
<option <?php if ($city2=="nameofregion2"){echo "SELECTED";}?> 
value="nameofregion2">nameofregion2</option>
<option <?php if ($northisland=="3"){echo "SELECTED";}?> 
value="3"></option>
</select>


from a php validation perspective if a user does not select any of 
the regions or both the regions i am displaying an error message 
asking them to either select 1 region from either city1 or city2

as of now there is a blank option being displayed which is working 
fine, i am having an issue with the php validation.

until i introduced value=0 my rules for validating the select tag 
were:

1. user cannot leave both the select tags with the default option 
which is "Select region1" & "Select region2"
2. user cannot select both the regions from city1 & city2 select tags

the code of 2. is 
	if(!($city1 == "region1") && !($city2 == "region2")) 
	{
	$error.="Please select only 1 Region<br />";
	}


now by introducing <option <?php if ($northisland=="0")
{echo "SELECTED";}?> value="0"></option> there is a conflict with 
the above php validation code used in point 2.

1. 
is it correct to use 1,2,3 as part of the following <option> tag or 
should i only use 0 everywhere
<option <?php if ($northisland=="0"){echo "SELECTED";}?> 
value="0"></option>
<option <?php if ($northisland=="1"){echo "SELECTED";}?> 
value="1"></option>

2.
how can i get around the conflict that is being created by 
introducing this value=0 with 
	if(!($city1 == "region1") && !($city2 == "region2")) 
	{
	$error.="Please select only 1 Region<br />";
	}
as i need the above php code and i also need the blank space for 
formatting purpose

please advice.

thanks.