## Regular expression for Even Length Strings defined over {a,b}

**Rule**

All strings having even length strings must be accepted and all other strings must be rejected by our Regular Expression.

**Regular expression=(aa+ab+ba+bb)***

## DFA for Regular expression of (aa+ab+ba+bb)*

**ACCEPTABLE STRINGS(PART OF THIS LANGUAGE)**

These strings are part of the given language and must be accepted by our Regular Expression.

- 3 strings of length 1 = no string exist.
- 4 strings of length 2 = {aa , ab , ba ,bb }
- 3 strings of length 3 = no string exist .
- 3 strings of length 4 = { aaba , aaaa , aabb, and many more similar strings}
- 3 strings of length 5 = no string exist.
- 3 strings of length 7= no string exist.
- 3 strings of length 10 ={aaaaababba,aaabbabbaa,babbaaabbb,bbaababbaa, and many more similar strings }
- 3 strings of length 15 = no string exist.
- 3 strings of length 20 = {aaaaaaababbababbbbaa,bababaabbaaaaabbabab,abababababbabaaaaaaa,bbbbbbbbaaaaaaaaabab,babababaabababababbb, and many more similar strings }
- 3 string of length 25 =no string exist.
- Many more similar strings

**Unacceptable strings(not part of this language)**

These strings are not part of the given language and must be rejected by our Regular Expression.

- 3 strings of length 1={a,b, and many more similar strings }
- 3 strings of length 3 = {aaa,bbb, and many more similar strings }
- 3 strings of lenth 5 ={aaaaa,bbbbb,aaaba, and many more similar strings }
- 3 strings of length 7 ={aaaaaaa,bbbbbbb,aaaaaab, and many more similar strings }
- 3 strings of length 15 ={aaaaaaaaaaaaaaa,ababaababababba,bbbbbbbbbbbbbb,babababababaaab, and many more similar strings }
- 3 strings of length 25={aaaaaaaaaaaaaaaaaaaaaaa,bbbbbbbbbbbbbbbbbbbbb,aaaaaabababababababababab, and many more similar strings }
- Many more similar strings.

## Download PPT Slides of Regular expression example

Regular expression for Even Length Strings defined over {a,b}

## More Examples of Regular Expression

- Regular Expression for no 0 or many triples of 0’s and many 1 in the strings.
- RegExp for strings of one or many 11 or no 11.
- A regular expression for ending with abb
- A regular expression for all strings having 010 or 101.
- Regular expression for Even Length Strings defined over {a,b}
- Regular Expression for strings having at least one double 0 or double 1.
- Regular Expression of starting with 0 and having multiple even 1’s or no 1.
- Regular Expression for an odd number of 0’s or an odd number of 1’s in the strings.
- Regular Expression for having strings of multiple double 1’s or null.
- Regular Expression (RE) for starting with 0 and ending with 1.
- RE for ending with b and having zero or multiple sets of aa and bb.
- A regular expression of the second last symbol is 1.
- RE for starting with 1 having zero or multiple even 1’s.
- Regular Expression for multiple a’s and multiple b’s.
- RE for exactly single 1 many 0’s |exactly single a many b.
- A regular expression for strings starting with aa and ending with ba.
- A regular expression for the language of all consecutive even length a’s.
- A regular expression for the language of all odd-length strings
- A regular expression for the language of all even length strings but ends with aa.
- A regular expression for the language of an odd number of 1s.
- A regular expression for the language of even length strings starting with a and ending with b in theory of automata.
- A regular expression for the language of all even length strings but starts with a.
- A Regular Expression for the Language of all strings with an even number of 0’s or even number of 1’s.
- A regular expression for the language of all those strings end with abb.
- A regular expression for string having must 010 or 101.
- Regular expression of strings begin with 110

Regular expression of strings begin and end with 110

Regular expression of strings containing exactly three consecutive 1’s. - A Regular Expression of all strings divisible by 4.
- A Regular Expression Strings that does not contain substring 110.

## Tutorial: Regular Expression

A detailed tutorial of the regular expression is here in the link of regular expression tutorial. This page contains the practice questions of regular expressions with solutions.

**Tutorial covering the topics**

- Give a regular expression.
- Describe the strings of the regular expression.
- write a regular expression.
- create all strings from regular expression.
- Generate all strings from regular expression.
- Extract all strings from regular expression.
- Find all strings from regular expression.
- Examples of regular expression.

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