Program to recognize a valid variable, which starts with a letter, followed by any number of letters or digits. | Compiler Design Lab Programs | Yacc Programs

Yacc Part :

%token DIGIT LETTER NL UND

%%

stmt : variable NL { printf(“Valid Identifiers\n”); exit(0);}

 ;

variable : LETTER alphanumeric

 ;

alphanumeric: LETTER alphanumeric

 | DIGIT alphanumeric

 | UND alphanumeric

 | LETTER

 | DIGIT

 | UND

 ;

%%

int yyerror(char *msg)

{

 printf(“Invalid Expression\n”);

 exit(0);

}

main ()

{

 printf(“Enter the variable name\n”);

 yyparse();

} 

Lex Part :

%{

 #include “y.tab.h”

%}

%%

[a-zA-Z] { return LETTER ;}

[0-9] { return DIGIT ; }

[\n] { return NL ;}

[_] { return UND; }

. { return yytext[0]; }

%%