C - Programming Guide

 %{
       #include<math.h>
       #include"y.tab.h"    //for left,right,up & down
%}
%%

[0-9]+|[0-9]*\.[0-9]+ {
                       yylval.p = atof(yytext);
                       return num;        //return nonterminal
                       }

sin {return SIN;}    //return token SIN to YACC
cos {return COS;}    //return token COS to YACC
tan return TAN;        //return token TAN to YACC
log return LOG;        //return token LOG to YACC
sqrt return SQRT;    //return token SQRT to YACC
[\t];
\n      return 0;
.       return yytext[0];


%%

 %{
       #include<stdio.h>
       #include<math.h>
%}

%union                //to define possible symbol types
{ double p;}
%token<p>num
%token SIN COS TAN LOG SQRT

/*Defining the Precedence and Associativity*/

%left '+','-'            //lowest precedence
%left '*','/'            //highest precedenc
%nonassoc uminu            //no associativity
%type<p>exp            //Sets the type for non - terminal

%%

/* for storing the answer */
ss: exp {printf("=%g\n",$1);}

/* for binary arithmatic operators */
exp :    exp'+'exp      { $$=$1+$3; }
       |exp'-'exp      { $$=$1-$3; }
       |exp'*'exp      { $$=$1*$3; }
       |exp'/'exp      {
                               if($3==0)
                               {
                                       printf("Divide By Zero");
                                       exit(0);
                               }
                               else $$=$1/$3;
                       }
       |'-'exp         {$$=-$2;}
       |'('exp')'      {$$=$2;}
       |SIN'('exp')'   {$$=sin($3);}
       |COS'('exp')'   {$$=cos($3);}
       |TAN'('exp')'   {$$=tan($3);}
       |LOG'('exp')'   {$$=log($3);}
       |SQRT'('exp')'  {$$=sqrt($3);}
       |num;
%%

/* extern FILE *yyin; */
main()
{
       do
       {
               yyparse();    /* repeatedly tries to parse the                 sentence until the i/p runs out */
       }while(1);

}

yyerror(s)            /* used to print the error message when an                 error is parsing of i/p */

char *s;
{
       printf("ERROR");
}