Lex program to recognize a valid arithmetic expression and to recognize the identifiers and operators present. Print them separately.
Problem definition:
Write a Lex Program to recognize a valid arithmetic expression. If the arithmetic expression is valid then recognize the identifiers and operators present in the expression and print identifiers and operators separately.
Structure of LEX Program:
| %{ Definition section %} %% Rules section %% User Subroutine section |
Click here to know – How to Compile & Run LEX / YACC Programs on Windows 8, 10, and 11?
Source Code to recognize a valid arithmetic expression and display operators and identifiers in it
%{
#include<stdio.h>
#include<string.h>
int flag=0,i=0,j,k=0;
char operand[20][20],oparator[20][20];
%}
%%
[a-zA-Z0-9]+ {flag++; strcpy(operand[i],yytext); i++;}
[-+*/] {flag--; strcpy(oparator[k],yytext); k++;}
%%
int main(int argc, char* argv[])
{
printf("enter an arithmetic expression\n");
yylex();
if(flag!=1)
printf("Invalid expression\n");
else
{
printf("Valid expression\n");
printf("The operands are\t");
for(j=0;j<i;j++)
printf("%s\t",operand[j]);
printf("\nThe operators are\t");
for(j=0;j<k;j++)
printf("%s\t",oparator[j]);
printf("\n");
}
}
int yywrap( )
{
return 1;
}Output:
input.c is the input file for the program
maheshgh@maheshgh:~/LexYacc$ lex demo.l
maheshgh@maheshgh:~/LexYacc$ gcc lex.yy.c
maheshgh@maheshgh:~/LexYacc$ ./a.out
Enter an arithmetic expression
a+b*c
Valid expression
The operands are a b c
The operators are + *
maheshgh@maheshgh:~/LexYacc$ ./a.out
Enter an arithmetic expression
a+b*
Invalid expression
Summary:
This article discusses how to write a Lex Program to recognize a valid arithmetic expression and to recognize the identifiers and operators present. Print them separately. If you like the article, do share it with your friends.