plz tell what is the difference in single and double comas ...in this case while assigning the value we had use 'tues'

Answer 1

whenever " .. " is used. The content inside it becomes a string. And when it is'..' the content remains a variable.we always use $_POST['NAME'];. THE NAME is a variable but it's inside a bracket so we use it with '..' so that it remains a variable only within a bracket

Answer 2

In Php, in one case escaping characters are evaluted, in the other case, they don't and keep them as is...

http://stackoverflow.com/questions/3446216/what-is-the-difference-between-single-quoted-and-double-quoted-strings-in-php