## Regular Expression (RE) for starting with 0 and ending with 1

Let us see the Regular Expression (RE) for starting with 0 and ending with 1 defined over {0,1}.

## Rule

All strings starting with 0 and ending with 1 must be accepted and all other strings must be rejected by our Regular Expression.

Regular Expression= 0(0+1)* 1

## DFA of the strings starting with 0 and ending with 1

**Rejected Strings (not part of the 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 strings}
- 3 strings of length 2 = {10, 00, 11}
- 3 strings of length 3 = {101, 110, 000}
- 3 strings of length 4 = {1001, 0110, 1000}
- 3 strings of length 7 = {01000, 10111, 11000}
- 3 strings of length 10 = {0000000000, 1111111111, 1000011110}
- 3 strings of length 15 = {000000000000000, 111111111111111, 100000001111110}
- 3 strings of length 20 = {10000000000000000000, 01111111111111111110, 10001110000001111111}
- 3 strings of length 25 = {1000000000001111100000001, 0111110000011111111111110, 1000111000111110001111110}
- Many other similar strigs.

## Acceptable strings (part of the 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 = {01, no more strings}
- 3 strings of length 3 = {001, 011, no more strings}
- 3 strings of length 4 = {0001, 0111,0011, 0101, no more strings }
- 3 strings of length 7 = {0000001, 0111111, 0000111, many other similar strigs}
- 3 strings of length 10 = {0000000001, 0111111111, 0000011111, many other similar strigs }
- 3 strings of length 15 = {000000000000001, 011111111111111, 000000001111111, many other similar strigs }
- 3 strings of length 20= {00000000000000000001, 01111111111111111111, 00001110000001111111, many other similar strigs }
- 3 strings of length 25 = {0000000000001111100000001, 0111110000011111111111111, 0000111000111110001111111, many other similar strigs }
- Many other similar strigs.

## Regular Expression (RE) for starting with a and ending with b

Let us see the Regular Expression (RE) for starting with a and ending with b defined over {a,b}.

**Rule: **

All strings starting with a and ending with b must be accepted and all other strings must be rejected by our Regular Expression.

**Regular Expression= a(a+b)* b **

## Rejected Strings (not part of the 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 strings}
- 3 strings of length 2 = {ba, aa, bb}
- 3 strings of length 3 = {bab, bba, aaa}
- 3 strings of length 4 = {baab, abba, baaa}
- 3 strings of length 7 = {abaaa, babbb, bbaaa}
- 3 strings of length 10 = {aaaaaaaaaa, bbbbbbbbbb, baaaabbbba}
- 3 strings of length 15 = {aaaaaaaaaaaaaaa, bbbbbbbbbbbbbbb, baaaaaaabbbbbba}
- 3 strings of length 20 = {baaaaaaaaaaaaaaaaaaa, abbbbbbbbbbbbbbbbbba, baaabbbaaaaaabbbbbbb}
- 3 strings of length 25 = {baaaaaaaaaaabbbbbaaaaaaab, abbbbbaaaaabbbbbbbbbbbbba, baaabbbaaabbbbbaaabbbbbba}
- Many other similar strigs

## Acceptable strings (part of the 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 = {ab, no more strings}
- 3 strings of length 3 = {aab, abb, no more strings}
- 3 strings of length 4 = {aaab, abbb,aabb, abab, no more strings }
- 3 strings of length 7 = {aaaaaab, abbbbbb, aaaabbb, many other similar strigs}
- 3 strings of length 10 = {aaaaaaaaab, abbbbbbbbb, aaaaabbbbb, many other similar strigs }
- 3 strings of length 15 = {aaaaaaaaaaaaaab, abbbbbbbbbbbbbb, aaaaaaaabbbbbbb, many other similar strigs }
- 3 strings of length 20= {aaaaaaaaaaaaaaaaaaab, abbbbbbbbbbbbbbbbbbb, aaaabbbaaaaaabbbbbbb, many other similar strigs }
- 3 strings of length 25 = {aaaaaaaaaaaabbbbbaaaaaaab, abbbbbaaaaabbbbbbbbbbbbbb, aaaabbbaaabbbbbaaabbbbbbb, many other similar strigs }
- Many other similar strigs.

## 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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