Let us see the Regular expression for all strings having 010 or 101 defined over {0,1}

**Regular expression=(0+1)*(010+101)(0+1)***

## DFA for Regular expression of (0+1)*(010+101)(0+1)*

**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.
- 3 strings of length 2 = no string exist
- 3 strings of length 3 = {101, 010,no more string} .
- 3 strings of length 4 = { 0101, 1011, 0100}.
- 3 strings of length 5 = {10101, 11011, 01010}.
- 3 strings of length 7= {1010110, 1101011, 1101110}.
- 3 strings of length 10 ={0000101011, 1000101001, 1101011011}.
- 3 strings of length 15 = {00001010100001, 011110100010001, 110101101100100}.
- 3 strings of length 20 = {0000101010000111000, 0111010001000100111, 11010110110010011100}.
- 3 string of length 25 ={000010101000011100011011, 011101000100010011100011, 1101011011001001110011010}.
- 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={1 ,0, no more string}.
- 3 strings of length 3 = {00,11,10}.
- 3 strings of lenth 5 ={11100,00000,01100}.
- 3 strings of length 7 ={1111000, 1100011, 0000111}.
- 3 strings og length 10 ={1111000111, 1110000111, 0000111100}.
- 3 strings of length 25={00001111111000011111, 1110000111100001110000000, 00001111110000011110000000}.
- Many more similar Strings.

## Regular expression for all strings having aba or bab

Let us see the Regular expression for all strings having aba or bab defined over {a,b}

# Regular expression=(a+b)*(aba+bab)(a+b)*

**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.
- 3 strings of length 2 = no string exist
- 3 strings of length 3 = {bab, aba,no more string} .
- 3 strings of length 4 = { abab, babb, abaa}.
- 3 strings of length 5 = {babab, bbabb, ababa}.
- 3 strings of length 7= {bababba, bbababb, bbabbba}.
- 3 strings of length 10 ={aaaabababb, baaababaab, bbababbabb}.
- 3 strings of length 15 = {aaaabababaaaab, abbbbabaaabaaab, bbababbabbaabaa}.
- 3 strings of length 20 = {aaaabababaaaabbbaaa, abbbabaaabaaabaabbb, bbababbabbaabaabbbaa}.
- 3 string of length 25 ={aaaabababaaaabbbaaabbabb, abbbabaaabaaabaabbbaaabb, bbababbabbaabaabbbaabbaba}.
- 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={b ,a, no more string}.
- 3 strings of length 3 = {aa,bb,ba}.
- 3 strings of lenth 5 ={bbbaa,aaaaa,abbaa}.
- 3 strings of length 7 ={bbbbaaa, bbaaabb, aaaabbb}.
- 3 strings og length 10 ={bbbbaaabbb, bbbaaaabbb, aaaabbbbaa}.
- 3 strings of length 25={aaaabbbbbbbaaaabbbbb, bbbaaaabbbbaaaabbbaaaaaaa, aaaabbbbbbaaaaabbbbaaaaaaa}.
- Many more similar Strings.

## Download Slides Presentation PPT

Regular expression for all strings having 010 or 101

## 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.