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:
Attention reader! Don’t stop learning now. Get hold of all the important CS Theory concepts for SDE interviews with the CS Theory Course at a student-friendly price and become industry ready.
