## What is the regular expression for the language of an odd number of 1s?

Regular expression for the language of an odd number of 1’s is given below.

^{∗}10^{∗}(0^{∗}10^{∗}10^{∗})^{∗} |

Now, let’s discuss that what strings should be accepted or rejected by our Regular Expression.

Accepted Strings |

You should check some small, some medium and some large size strings that are part of the language and all of them(100% strings) should be accepted by our R.E. |

Small strings:
1, 01, 10, 010, 001, 100, 111, 1011 …… and all such strings that contain odd numbers of 1’s in the strings. |

Medium size strings:
100100001, 11000001, 10110011,……and all such strings that contain odd numbers of 1’s in the strings. |

Large size strings:
100000000100000001, 110001011100100000,…….and all such strings that contain odd numbers of 1’s in the string. |

Rejected Strings |

You should check some small, some medium and some large size strings that are not part of the language and all of them(100% strings) should be rejected by our R.E. |

Small strings:0, 00, 11, 011, 101, 100, 110, 1111 …… and all such strings that are not part of our language( does not contains odd numbers of 1’s in the strings). |

Medium size strings:
1000001, 0100100101, 111100011 …… and all such strings that are not part of our language (does not contains odd numbers of 1’s in the strings). |

Large size strings:
100000000100000011, 110001011100110000,…….and all such strings that do not contain odd numbers of 1’s in the string(not part of the language). |

## Finite Automata for the language of an odd number of 1s

## RegEx for odd length a’s defined over {a, b}.

RE ⇒ b+ a(a b* a)*

**valid strings: **a, b, aaa, aaaaa, abaa, ……and many more similar strings.

**invalid strings: **aa, aaaa, aba, ……and many more similar strings.

## RegEx for odd length b’s defined over {a, b}.

RE ⇒ a+b(b a* b)*

## RegEx for odd length 1’s defined over {0, 1}.

RE ⇒ 0+1(1 0* 1)*

## RegEx for odd length 0’s defined over {0, 1}.

RE ⇒ 1+0(0 1* 0)*

## 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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