S6 CS COMPILER LAB : ARITHMETIC EXPRESSION VALIDATION

/*  ARITHMETIC EXPRESSION VALIDATION  */

Yacc program

%{

#include<stdio.h>

#include<stdlib.h>

%}

%token num alpha

%left '+''-'

%left '*''/'

%right '^'

%nonassoc UMINUS

%%

S:E NL  { printf("\nThe given expression is valid\n");exit(0);}

E:E'+'E

 |E'-'E

 |E'*'E

 |E'/'E

 |'-'E %prec UMINUS

 |'('E')'

 |E'^'E

 |num

 |alpha

 ;

%%

#include"lex.yy.c"

int main()

{

yyparse();

yylex();

return 0;

}

yyerror(char *s)

{

 printf("\nThe given expression is invalid\n");

}

Lex program

%{

#include"y.tab.h"

%}

%%

[0-9]+    {return num;}

[a-z]+    {return alpha;}

[ \t]      ;

[\n]      {return NL;}

.         {return yytext[0];}

%%

 OUTPUT

-8+4

The given expression is valid

(4*2

The given expression is invalid