While Loop

Using lex-yacc check while loop statement in a C program

YACC FILE

Source Code:
%{
#include
void yyerror(char *);
int yylex();
%}

%token WHILE AND OR NTEQ EQ LT LTEQ GT GTEQ ID NUM
%%
whileloop	: WHILE '(' cond ')' '{' '}' {printf("parsing successful");}
	;

cond	: scond
	| scond logop cond
	;

scond	: nid
	| nid relop nid
	;

nid	: ID
	| NUM
	;

logop	: AND
	| OR
	;

relop	: NTEQ
	| EQ
	| LT
	| LTEQ
	| GT
	| GTEQ
	;

%%

void yyerror(char *s)
{
	printf("\nparsing err ");
}

int main()
{
	yyparse();
	return 0;
}


Lex FILE

Source Code:
 %{
#include "y.tab.h"
void yyerror(char *);
%}

%%
"while" {return WHILE;}
"&&" {return AND;}
"||" {return OR;}
"!=" {return NTEQ;}
"==" {return EQ;}
"<"  {return LT;}
"<=" {return LTEQ;}
">"  {return GT;}
">=" {return GTEQ;}

[=,{}();] {return *yytext;}
[ \t\n]+ ;
[a-zA-Z_][a-zA-Z0-9_]* {return ID;}
[0-9]+ {return NUM;}
. {printf("\n\nlex err");}
%%
int yywrap()
{
return 1;
}
OUTPUT:

[cmsa@localhost whileloop]$ yacc -d while.y
[cmsa@localhost whileloop]$ lex while.l
[cmsa@localhost whileloop]$ cc lex.yy.c y.tab.c -o a
[cmsa@localhost whileloop]$ ./a