Regexes for integer constants and for binary numbers

Question

Hi, I have tried 2 questions, could you tell me whether I am right or not?

1. Regular expression of nonnegative integer constants in C, where numbers beginning with 0 are octal constants and other numbers are decimal constants.

   I tried 0([1-7][0-7]*)?|[1-9][0-9]*, is it right? And what string could I match? Do you think 034567 will match and 000083 match?

2. What is a regular expression for binary numbers x such that h^x + i^x = j^x?

I tried (0|1){32}|1|(10)).. do you think a string like 10 will match and 11 won’t match?

Please tell me whether I am right or not.

Answer 1

Your regex for integer constants will not match base-10 numbers longer than two digits and octal numbers longer than three digits (2 if you don't count the leading zero). Since this is a homework, I leave it up to you to figure out what's wrong with it.

Hint: Google for "regular expression repetition quantifiers".

Answer 2

1. 0([1-7][0-7])?|[1-9][0-9] is wrong because there's no repetition - it will only match 1 or 2-character strings. What you need is something like 0[0-7]*|[1-9][0-9]*, though that doesn't take hexadecimal into account (as per spec).
2. This one is not clear. Could you rephrase that or give some more examples?

Answer 3

You can always use http://www.spaweditor.com/scripts/regex/ for a quick test on whether a particular regex works as you intend it to. This along with google can help you nail the regex you want.

Answer 4

max answered the first question.

the second appears to be the unsolvable diophantine equation of fermat's last theorem. if h,i,j are non-zero integers, x can only be 1 or 2, so you're looking for

^0*10?$

does that help?

Answer 5

There are several tool available to test regular expressions, such as The Regulator.

If you search for "regular expression test" you will find numerous links to online testers.