S6 CSE COMPILER LAB : PARSER FOR IF THEN ELSE STATEMENT

                       /* PARSER FOR IF THEN ELSE STATEMENT  */

Yacc program

%{

#include<stdio.h>

#include<stdlib.h>

%}

%token num alpha LT GT EQ LE GE NE AND OR NL IF ELSE INC DEC

%left '+''-'

%left '*''/'

%right '^'

%right '='

%nonassoc UMINUS

%nonassoc IF

%nonassoc ELSE

%left LT GT EQ LE GE NE

%left AND OR

%%

S:ST NL  {printf("ACCEPTED\n");exit(0);}

ST:IF'('F')''{'ST'}' %prec IF

     |IF'('F')''{'ST'}'ELSE'{'ST'}'

     |E';'ST

     |E';'

F:C LO C

  |C

LO:AND

     |OR

C:E RELOP E

E:alpha'='E

   |E'+'E

   |E'-'E

   |E'*'E

   |E'/'E

   |E'^'E

   |'-'E %prec UMINUS

   |alpha

   |num

   |alpha INC

   |alpha DEC

RELOP:LT

             |GT

             |EQ

             |GE

             |LE

             |NE

             ;

%%

#include"lex.yy.c"

#include<stdio.h>

int main()

{

  yyparse();

  yylex();

  return 0;

}

yyerror(char *s)

{

  printf("Error\n");

}

Lex program

%{

#include "y.tab.h"

%}

%%

"if"     {return IF;}

"else" {return ELSE;}

"&&" {return AND;}

"||"      {return OR;}

"<"     {return LT;}

">"     {return GT;}

"<="               {return LE;}

">="               {return GE;}

"!="                {return NE;}

"=="               {return EQ;}

"++"               {return INC;}

"--"                 {return DEC;}

[a-z]+               {return alpha;}

[0-9]+    {return num;}

[ \t]       ;

[\n]      {return NL;}

.           {return yytext[0];}

%%

 OUTPUT

if(a>b){a;}

ACCEPTED

if(a==b){c=a+b;}else{c=a-b;}

ACCEPT ED

if(a>b){c=a}else{c=b}

ERROR