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IMPLEMENTATION OF CALCULATOR USING LEX AND YACC

Ex. No : 11

IMPLEMENTATION OF CALCULATOR USING LEX AND YACC

Date : 17.04.2024

AIM

To implement a calculator using LEX and YACC.

ALGORITHM

1. Start the program.
2. Write a program in the vi editor and save it with .l extension.
3. In the lex program, write the translation rules for the various mathematical functions.
4. Write a program in the vi editor and save it with .y extension.
5. Compile the lex program with lex compiler to produce output file as lex.yy.c. eg $ lex filename.l
6. Compile the yacc program with yacc compiler to produce output file as y.tab.c. eg $ yacc –d arith_id.y
7. Compile these with the C compiler as gcc lex.yy.c y.tab.c
8. Enter an expression as input and it is evaluated and the answer is displayed as output.

PROGRAM

Lex File (calculator.l)

%{
#include "y.tab.h"
#include <math.h>
%}

%%
([0-9]+|([0-9]*\.[0-9]+)([eE][-+]?[0-9]+)?) { yylval.dval = atof(yytext); return NUMBER; }
log|LOG { return LOG; }
ln|LN { return nLOG; }
sin|SIN { return SINE; }
cos|COS { return COS; }
tan|TAN { return TAN; }
mem { return MEM; }
[\t] ;
\$ return 0;
\n|. return yytext[0];
%%

Yacc File (calculator.y)

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

double memvar;
%}

%union { double dval; }

%token <dval> NUMBER
%token <dval> MEM
%token LOG nLOG SINE COS TAN
%left '-' '+'
%left '*' '/'
%right '^'
%left LOG nLOG SINE COS TAN

%nonassoc UMINUS
%type <dval> expression

%%

start: statement '\n'
| start statement '\n'
;

statement: MEM '=' expression { memvar = $3; }
| expression { printf("Answer = %g\n", $1); }
;

expression: expression '+' expression { $$ = $1 + $3; }
| expression '-' expression { $$ = $1 - $3; }
| expression '*' expression { $$ = $1 * $3; }
| expression '/' expression { 
    if ($3 == 0)
        yyerror("Error: Divide by zero");
    else
        $$ = $1 / $3; 
}
| expression '^' expression { $$ = pow($1, $3); }
| '-' expression %prec UMINUS { $$ = -$2; }
| '(' expression ')' { $$ = $2; }
| LOG expression { $$ = log($2) / log(10); }
| nLOG expression { $$ = log($2); }
| SINE expression { $$ = sin($2 * M_PI / 180); }
| COS expression { $$ = cos($2 * M_PI / 180); }
| TAN expression { $$ = tan($2 * M_PI / 180); }
| NUMBER { $$ = $1; }
| MEM { $$ = memvar; }
;

%%

C Program (main.c)

#include "y.tab.h"
#include <stdio.h>

int main() {
    printf("Enter the expression: ");
    yyparse();
    return 0;
}

int yyerror(char *error) {
    printf("%s\n", error);
    return 0;
}

OUTPUT

RESULT

The calculator is implemented using LEX and YACC and the output is verified.