but if i want to know the words which ends with "f"
Mach exactly what you want, not more. A . matches non-word characters, which is bad in your case. Try \b\w*f\b instead.
also i want to know the words wich does not begin with "f" but have at least one "f" in the remainder of the word:
\b[^f]\w*f\w*\b might be worth a try, but I'm not convinced it's strict enough. Maybe \b(?=\w)[^f]\w*f\w*\b is right for you

(All examples here untested).

Update: ysth++ pointed out that (?=\w)[^f] is better written as [^f\W] - and indeed it is, if you consider only ASCII semantics. When you use Unicode, \w is not the same as [^\W].

In reply to Re: words wich ends with "f" by moritz
in thread words wich ends with "f" by Anonymous Monk

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