>>I would like to know that what is the difference between single quotation Mark and double. please logically justify the both why we use single quote and double quote.

>I use Single QUotes cause its less keystrokes. If not possible (cause of an apostrophe) I have to use either " or [. One note, everyone says that quotes and brackets are the same, but thats not completley true.

>Run this code

>#DEFINE ccVar variable!
>?"hey, whats the name of that ccVar"
>?[hey, whats the name of that ccVar]

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just to add to what Mike has already said, how about these:
? "hey, you have pressed the 'delete' button"
? [The user "Mike" has pressed the 'delete' button]

IOW, having these multiple ways of specifying quotes allows an easy way to use quotes w/o being interpreted as quotes!

This techique is often used when creating commands which will be expanded later.
for example:
cQuery = [select * from customer where state = "FL"]
&cQuery (not suggesting this type of macro use is good technique)

Hope this helps, Mohammed!