Regular expression for the language of even length strings starting with a and ending with b.

**Accepted Strings: **

All strings of the following pattern should be accepted by RE.

ab, aab, abb,abab,……

**Reject strings:**

All strings of the following pattern should be rejected by RE.

a, b, ba, aa, bb, ba,bba,……

**R.E =** a (aa+bb+ab+ba)* b

## Deterministic Finite Automata for the language of even length strings starting with a and ending with b

## Regular expression for even number of a’s defined over {a,b}

regular expression for even number of a’s is (b|ab*ab*)*.

**Valid strings:** aa, aba, aab, aaaab, aaaba, aabaa, abaaa, baaaa,…. and many other similar strings.

**Invalid strings:** ab, ba, aaa, aaab, aaba, aaba, abaa, baaa,…. and many other similar strings.

## A regular expression for the language of all those strings having just ab or if string size is greater than 2, then

starting with ab and ending with b and having even length strings

## A regular expression for the language of all those strings

starting with ab and ending with b and having even length strings

ab(a+b)((a+b)(a+b))*b

## Regular expression for even number of b’s defined over {a,b}

regular expression for even number of b’s is (a|ba*ba*)*.

## All strings having at least two occurences of the substring 00

((1 + 0)*00(1 + 0)*00(1 + 0)*)^{+}

**Valid strings:** 0000, 10000, 00001, 100100, 110000, 000011, …. and many other similar strings.

**Invalid strings:** 0, 00, 01, 10, 001, 100, 0100, 1000, 00000, 1000, 0001, 10100, 11000, 00011, …. and many other similar strings.

## 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.