%{
#include <stdio.h>
#define YYERROR_VERBOSE
void yyerror(char *);
%}
%token NUMBER ILLEGAL_CHAR
%left '-' '+'
%left '*' '/'
%%
eingabe:          /* empty */
                | eingabe berechnung
                ;
berechnung:       term '=' { printf("Ergebnis: %d\n", $1); }
                ;
term:             NUMBER
                | term '+' term { $$ = $1 + $3; }
                | term '-' term { $$ = $1 - $3; }
                | term '*' term { $$ = $1 * $3; }
                | term '/' term { $$ = $1 / $3; }
                | '(' term ')' { $$ = $2; }
                ;
%%
void yyerror(char *msg) {
    printf("\nEingabefehler: %s\n", msg);
}
int main() {
    return yyparse();
}