Syntax help

Hi All.
 
What is the correct syntax in windows for extension_dir = 
In my case the path is c:\php\ext
 
Im just wondering if my syntax is correct  
 
extension_dir = "c:\php\ext" 
 
Or should it be extension_dir = c:\php\ext
 
Or maybe extension_dir = "c:/php/ext"
 
Im asking cause Ive seen them all used when goggling a problem im having
with My php_gd2.dll