%{
   #include<stdio.h>
   int yylex(void);
   void yyerror(char *);
   int sym[26]
%}
%token INTEGER VARIABLE
%left '+' '-'
%left '*' '/'
%left '(' ')'

%%
program:
program expr '\n' { printf("%d\n", $2);}
|
;
expr:
expr {printf("%d\n",$1);}
|VARIABLE'='expr{sym[$1]=$3;}
;
expr:
INTEGER 
variable{$$=sym[$1];}
| expr '+' expr { $$ = $1 + $3; }
| expr '-' expr { $$ = $1 - $3; }
| expr '*' expr { $$ = $1 * $3; }
| expr: '(' expr ')' {$$ = $2;}
| expr '/' expr { if($3==0)
                  yyerror("divided by zero\n");
                  else
                  $$ = $1 / $3; }
;
%%
void yyerror(char *s){
    fprintf(stderr, "%s\n", s); 
}
int main(void){
        yyparse();
        return 0;
}