Theory of computationːRegular languages
< A-level Computing | AQA | Paper 1 | Theory of computation
- Finite State Machines with and without Output (Mealy Machines)
- Maths for Regular Expressions
- Regular Expressions
- Regular Languages
- Backus-Naur Form for Context-Free Languages
A regular expression is an expressions used to specify a set of strings that satisfy given conditions (A sequence of characters that define a search pattern). They are used by programmers and computers to work with text patterns. The most popular implementations are in search engines and search & replace dialogues in word processors.
Most programming languages support regular expressions, but the most common symbols are described below:
- | A vertical bar separates alternatives e.g. (D|d)is(c|k)
- ? A question mark indicates zero or one of the preceding element e.g. colou?r
- * An asterisk indicates zero or more of the preceding element e.g. aa and aabbb would match aab*
- + A plus indicates one or more of the preceding element e.g. abc and abccc would match abc+
If your programming language supports regular expressions, such as Python, the syntax might be different.