If Statement

Using lex-yacc check if statement in a C program

YACC FILE

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

%token IF ELSE AND OR NTEQ EQ LT LTEQ GT GTEQ ID NUM
%%
if_stmt	: ifp elsep {printf("parsing successful");}
	;

ifp	: IF '(' cond ')' '{' '}'
	;

elsep	: ELSE '{' '}'
	;

cond	: scond
	| scond logop cond
	;

scond	: mid
	| mid relop mid
	;

mid	: 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 *);
%}

%%
"if" {return IF;}
"else" {return ELSE;}
"&&" {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:

[cmsa1@localhost ifstatement]$ yacc -d if.y
[cmsa1@localhost ifstatement]$ lex if.l
[cmsa1@localhost ifstatement]$ cc y.tab.c lex.yy.c -o a
[cmsa1@localhost ifstatement]$ ./a<a1
parsing successful[cmsa1@localhost ifstatement]$