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Which engine/language are you using? I am not familiar with that syntax for OR expressions.
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Which engine/language are you using? I am not familiar with that syntax for OR expressions.

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well, i'm not sure what it is, this is part of my homework and these are details which I got:<br />
( and ) are for grouping<br />
* means any number of occurrences (including none)<br />
+ means at least one occurrence<br />
? means at most one occurrence<br />
{a, b, c} represents a or b or c<br />
@ matches any word or part of speech<br />
a,b,c means a followed by b followed by c <br />
<br />
I think it is something like: I ?{a} passed, but I'm not sure:/
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well, i'm not sure what it is, this is part of my homework and these are details which I got:
( and ) are for grouping
* means any number of occurrences (including none)
+ means at least one occurrence
? means at most one occurrence
{a, b, c} represents a or b or c
@ matches any word or part of speech
a,b,c means a followed by b followed by c

I think it is something like: I ?{a} passed, but I'm not sure:/

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Actually, punctuation may not be of concern for this problem. I don't know what your valid inputs are, though.
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Actually, punctuation may not be of concern for this problem. I don't know what your valid inputs are, though.

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Hi, <br />
I know that {a, b, c} represents a or b or c.<br />
How can I write regular expression for to accepts sentences &quot;I passed&quot; and &quot;I had passed&quot;.<br />
Is it just {a} or {a, &quot;&quot;} or something different?
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Hi, 
I know that {a, b, c} represents a or b or c.
How can I write regular expression for to accepts sentences "I passed" and "I had passed".
Is it just {a} or {a, ""} or something different?

regex - value a or nothing

A regular expression ("regex") is a sequence of characters that define a search pattern, mainly for use in pattern matching with strings, or string matching, i.e. "find and replace"-like operations. Regular expression processors are found in several search engines, search and replace dialogs of several word processors and text editors, and in the command lines of text processing utilities, such as sed and AWK. Many programming languages provide regular expression capabilities, some built-in, for example Perl, JavaScript, Ruby, AWK, and Tcl, and others via a standard library, for example .NET languages, Java, Python and C++ (since C++11). Most other languages offer regular expressions via a library.