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Lex Program to count number of words

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  • Difficulty Level : Basic
  • Last Updated : 13 Mar, 2023
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Lex is a computer program that generates lexical analyzers and was written by Mike Lesk and Eric Schmidt.
Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language.
Prerequisite: Flex (Fast lexical Analyzer Generator)


Input: Hello everyone
Output: 2

Input: This is GeeksforGeeks
Output: 3

Note: The words can consist of lowercase characters, uppercase characters and digits.

Below is the implementation to count the number of words.

/*lex program to count number of words*/
int i = 0;
/* Rules Section*/
([a-zA-Z0-9])*    {i++;} /* Rule for counting 
                          number of words*/
"\n" {printf("%d\n", i); i = 0;}
int yywrap(void){}
int main()
    // The function that starts the analysis
    return 0;


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