If Query String "id" is EMpty then id=0 (If else condition)

[darubillah]

hi,

 

i want a little help, i am making a site in which i also added a referral system

 

now I want to create an IF ELSE condition

 

for eg

 

<a href="index.php?id=<? echo $_GET["id"]; ?>">HOME</a>

 

now if some one refers to my page it will get id from QUERY STRING

 

but I want that if someone not refers him, or he come from googling or direct

 

then the value of QUERY STRING id will be " 0" ,,, id=0

 

can anyone tell me how to do this

 

thankyou best Regards

Shayan

[darubillah]

I made this and it working

 

<a href="index.php?id=<? if($_GET["id"]==null) { echo "0"; } else { echo $_GET["id"]; } ?>">HOME</a>