S6 CS-COMPILER LAB : ARITHMETIC EXPRESSION EVALUATION

 /*  ARITHMETIC EXPRESSION EVALUATION  */

Yacc program

%{

 #include<stdio.h>

 #include<stdlib.h>

 int i;

%}

%token num alpha NL

%left '+''-'

%left '*''/'

%right '^'

%nonassoc UMINUS

%%

S:E NL           {printf("The answer is =%d\n",$$);exit(0);}

E:E'+'E {$$=$1+$3;}

   |E'-'E {$$=$1-$3;}

   |E'*'E {$$=$1*$3;}

   |E'/'E {$$=$1/$3;}

   |'-'E %prec UMINUS  {$$=-$2;}

   |'('E')'  {$$=$2;}

   |E'^'E  {if($3==0)

           $$=1;

          else

          {

           $$=1;

           for(i=1;i<=$3;i++)

            $$=$$*$1;}

          }

   |num {$$=$1;}

   ;

%%

#include"lex.yy.c"

#include<stdio.h>

int main()

{

  yyparse();

  yylex();

  return 1;

}

yyerror(char *s)

{

  printf("\nError\n");

}

Lex program

%{

 #include "y.tab.h"

%}

%%

[0-9]+  {yylval=atoi(yytext);return num;}

[ \t]      ;

[\n]      {return NL;}

.           {return yytext[0];}

%%

                                                            

 OUTPUT

(2*3)/2+4-1

The answer is =6

(4*3)-(2*2)+5-1

The answer is =12