Lex program to check if a Date is valid or not
Problem: Write a Lex program to check if a date is valid or not.
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.
Note: Format of Date is DD/MM/YYYY.
Examples:
Input: 02/05/2019 Output: It is a valid date Input: 05/20/2019 Output: It is not a valid date
Implementation:
/* Lex program to check if a date is valid or not */ %{ /* Definition section */ #include<stdio.h> int i=0, yr=0, valid=0; %} /* Rule Section */ %% ([0-2][0-9]|[3][0-1])\/((0(1|3|5|7|8))|(10|12)) \/([1-2][0-9][0-9][-0-9]) {valid=1;} ([0-2][0-9]|30)\/((0(4|6|9))|11) \/([1-2][0-9][0-9][0-9]) {valid=1;} ([0-1][0-9]|2[0-8])\/02 \/([1-2][0-9][0-9][0-9]) {valid=1;} 29\/02\/([1-2][0-9][0-9][0-9]) { while (yytext[i]!= '/' )i++; i++; while (yytext[i]!= '/' )i++;i++; while (i<yyleng)yr=(10*yr)+(yytext[i++]- '0' ); if (yr%4==0||(yr%100==0&&yr%400!=0))valid=1;} %% // driver code main() { yyin= fopen ( "vpn.txt" , "r" ); yylex(); if (valid==1) printf ( "It is a valid date\n" ); else printf ( "It is not a valid date\n" ); } int yywrap() { return 1; } |
Output:
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