Lex program to check valid Mobile Number Last Updated : 17 May, 2019 Improve Improve Like Article Like Save Share Report Problem: Write a Lex Program to check valid Mobile Number. Explanation: 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. Examples: Input: 7017175023 Output: Mobile Number Valid Input: 0001112223 Output: Mobile Number Invalid Implementation: /* 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 : "); yylex(); printf("\n"); return 0; } Output: Like Article Suggest improvement Previous YACC program to implement a Calculator and recognize a valid Arithmetic expression Next DFA in LEX code which accepts Odd number of 0’s and even number of 1’s Share your thoughts in the comments Add Your Comment Please Login to comment...