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Lex Program to accept string starting with vowel

  • Last Updated : 30 Apr, 2019
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Lex is a computer program that generates lexical analyzers. Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language.

The commands for executing the lex program are:

lex abc.l (abc is the file name)
cc lex.yy.c -efl
./a.out 

Let’s see lex program to accept string starting with vowel.
Examples:

Input: animal
Output: Accepted

Input: zebra
Output: Not Accepted 

Below is the implementation:




/* Lex Program to accept string starting with vowel */
% {
  int flag = 0;
% }
  
%%
  
[aeiouAEIOU].[a-zA-Z0-9.]+ flag=1;
[a-zA-Z0-9]+
  
%%
  
main()
{
 yylex();
 if (flag == 1) 
    printf("Accepted"); 
 else
    printf("Not Accepted"); 
}

Output:

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