Implementation of Calculator using lex and yacc

file name Cal.l 




%{
#include<stdio.h>
#include "y.tab.h"
//extern int yylval;
%}

%%

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

[\n] return 0;
. return yytext[0];

%%

int yywrap()
{
return 1;
}



file name  cal.y


%{
#include<stdio.h>
int flag=0;
%}

%token NUMBER
%left '+' '-'
%left '*' '/' '%'
%left '(' ')'

%%

ArithmeticExpression: E{

         printf("\nResult=%d\n",$$);
         return 0;
        };

E:E'+'E {$$=$1+$3;}
 |E'-'E {$$=$1-$3;}
 |E'*'E {$$=$1*$3;}
 |E'/'E {$$=$1/$3;}
 |E'%'E {$$=$1%$3;}
 |'('E')' {$$=$2;}
 | NUMBER {$$=$1;}
;

%%
int main()
{
  yyparse();
  if(flag==0)
   printf("\nEntered arithmetic expression is Valid\n\n");
  return 0;
}

int yyerror()
{
   printf("\nEntered arithmetic expression is Invalid\n\n");
   flag=1;
   return 0;
}



output :




rach@rach-virtual-machine:~/Compilers/Calc$ lex Calc.l
rach@rach-virtual-machine:~/Compilers/Calc$ yacc -d Calci.y
rach@rach-virtual-machine:~/Compilers/Calc$ cc lex.yy.c y.tab.c
rach@rach-virtual-machine:~/Compilers/Calc$ ./a.out
4+5    

Result=9

Entered arithmetic expression is Valid

rach@rach-virtual-machine:~/Compilers/Calc$ ./a.out
4+

Entered arithmetic expression is Invalid

rach@rach-virtual-machine:~/Compilers/Calc$ ./a.out
+6

Entered arithmetic expression is Invalid


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