Program to check the syntax of a simple expression involving operators +, -, * and / . | Compiler Lab Programs | Yacc Programs

Yacc Part :

%token NUMBER ID NL

%left ‘+’ ‘-‘

%left ‘*’ ‘/’

%%

stmt : exp NL { printf(“Valid Expression”); exit(0);}

 ;

exp : exp ‘+’ exp

 | exp ‘-‘ exp

 | exp ‘*’ exp

 | exp ‘/’ exp

 | ‘(‘ exp ‘)’

 | ID

 | NUMBER

 ;

%%

int yyerror(char *msg)

{

 printf(“Invalid Expression\n”);

 exit(0);

}

main ()

{

 printf(“Enter the expression\n”);

 yyparse();

} 

Lex Part :

%{

 #include “y.tab.h”

%}

%%

[0-9]+ { return NUMBER; }

[a-zA-Z][a-zA-Z0-9_]* { return ID; }

\n { return NL ;}

. { return yytext[0]; }

%%