Lex (Lexical Analyzer Generator) is a tool used to generate lexical analyzers (also known as tokenizers or scanners) for processing text input. Lex helps in breaking down input text into a sequence of tokens, which are then used by parsers and other components of a compiler or text processing system. Lex operates by defining regular expressions and associated actions to handle different patterns in the input text. Here are some commonly used Lex functions along with examples: 1. **Regular Expression Definitions:** Lex allows you to define regular expressions that match specific patterns in the input text. These regular expressions are used to identify tokens. ```lex %% [0-9]+ { printf("NUM: %s\n", yytext); } [a-zA-Z]+ { printf("ID: %s\n", yytext); } ``` In this example, the regular expression `[0-9]+` matches sequences of digits (numbers), and `[a-zA-Z]+` matches s...