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Lex code for password validation
  • Last Updated : 25 Jun, 2019

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 lex in the C programming language.

Problem: We have to validate password.
A password is correct if it contains:

  1. Atleast 1 uppercase character
  2. Atleast 1 lowercase character
  3. Atleast 1 digit
  4. Atleast 1 special character
  5. Minimum 8 characters

Example:

Input: Geeksforgeeks
Output: INVALID

Input: Geeks@12
Output: VALID 

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

Below is the implementation to count the number of words.



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%{ 
    #include<stdio.h> 
    #include<string.h> 
    int a = 0, b=0, c=0, d=0, l=0; 
%} 
    
  
%% 
[a-z]    {a++;l++;}
[A-Z]    {b++;l++;}
[0-9]    {c++;l++;}
[$&+, :;=?@#|'<>.-^*()%!] {d++;l++;}
.  ;
%% 
    
int yywrap(void){} 
    
int main() 
{    
    // The function that starts the analysis 
    yylex(); 
      if(a>0 && b>0 && c>0 && d>0 && l>=8)
    printf("VALID\n");
    else
        printf("INVALID\n");
    return 0; 

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Output:



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