parser.y

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

    void yyerror(const char *s);
    int yylex();
%}

%union {
    int num;  /* Define a type for numerical values */
}

%token <num> NUMBER
%token PLUS MINUS MULTIPLY DIVIDE LPAREN RPAREN
%left PLUS MINUS
%left MULTIPLY DIVIDE
%right UMINUS

%type <num> expr  /* Associate expr with int type */

%%

expr:
      expr PLUS expr      { $$ = $1 + $3; printf("Result: %d\n", $$); }
    | expr MINUS expr     { $$ = $1 - $3; printf("Result: %d\n", $$); }
    | expr MULTIPLY expr  { $$ = $1 * $3; printf("Result: %d\n", $$); }
    | expr DIVIDE expr    { 
        if ($3 == 0) { 
            printf("Error: Division by zero\n"); 
            $$ = 0;
        } else {
            $$ = $1 / $3; 
            printf("Result: %d\n", $$);
        }
      }
    | LPAREN expr RPAREN  { $$ = $2; }
    | MINUS expr %prec UMINUS { $$ = -$2; }
    | NUMBER              { $$ = $1; }
    ;

%%

void yyerror(const char *s) {
    fprintf(stderr, "Error: %s\n", s);
}

int main() {
    printf("Enter an expression:\n");
    return yyparse();  // Calls the Bison parser
}