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Lex program to check valid Mobile Number

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  • Difficulty Level : Basic
  • Last Updated : 17 May, 2019
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Problem: Write a Lex Program to check valid Mobile Number.

FLEX (Fast Lexical Analyzer Generator) is a tool/computer program for generating lexical analyzers (scanners or lexers) written by Vern Paxson in C around 1987. Lex reads an input stream specifying the lexical analyzer and outputs source code implementing the lexer in the C programming language. The function yylex() is the main flex function which runs the Rule Section.


Input: 7017175023
Output: Mobile Number Valid

Input: 0001112223
Output: Mobile Number Invalid 


/* Lex Program to check valid Mobile Number */
    /* Definition section */
/* Rule Section */
[1-9][0-9]{9} {printf("\nMobile Number Valid\n");}
.+ {printf("\nMobile Number Invalid\n");}
// driver code 
int main() 
    printf("\nEnter Mobile Number : ");
    return 0;


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