z.y calculator parser

%{
#include <stdio.h>
#include <stdlib.h>
#include "y.tab.h"
#include "lex.yy.c"
double symbolTable[4];
double *arrayTable[4] = {NULL, NULL, NULL, NULL};
int arraySize[4] = {0};
void yyerror(char const *);
%}
%union{
  int ival;
  double dval;
}
%token <ival> ID ID2
%token <dval> NUM
%type <dval> Expr
%token PRT DIM
%left '+' '-'
%left '/' '*' '%' QUO
%start Program
%%
Program: Statement
       | Program Statement
       ;
Statement: Assign ';'
         | Print ';'
         | Decl ';'
         ;
Assign: ID '=' Expr { symbolTable[$1] = $3; }
      | ID2 '[' Expr ']' '=' Expr {
            if (arraySize[$1] <= 0) {
                yyerror("no initialize.");
            } else if ($3 < 0 || arraySize[$1] <= $3) {
                yyerror("index error.");
            } else {
                arrayTable[$1][(int )$3] = $6;
            }
        }
      ;
Print: PRT Expr { printf("%f\n", $2); }
     ;
Decl: DIM ID2 '[' Expr ']' {
          if (arraySize[$2] > 0) {
              yyerror("almost declared.");
          } else if ($4 < 0) {
              yyerror("index error.");
          } else {
              int n = $4;
              arraySize[$2] = n;
              double *p = arrayTable[$2] = calloc(sizeof *p, n);
              for (int i = 0; i < n; ++i) {
                  p[i] = 0.;
              }
          }
      }
    ;
Expr: Expr '+' Expr { $$ = $1 + $3; }
    | Expr '-' Expr { $$ = $1 - $3; }
    | Expr '*' Expr { $$ = $1 * $3; }
    | Expr '/' Expr { $$ = $1 / $3; }
    | Expr '%' Expr { $$ = (int )$1 % (int )$3; }
    | Expr QUO Expr { $$ = (int )$1 / (int )$3;}
    | '(' Expr ')' { $$ = $2; }
    | NUM { $$ = $1; }
    | ID { $$ = symbolTable[$1]; }
    | ID2 '[' Expr ']' {
          if (arraySize[$1] <= 0) {
              yyerror("no initialize.");
              $$ = 0.;
          } else if ($3 < 0 || arraySize[$1] <= $3) {
              yyerror("index error.");
              $$ = 0.;
          } else {
              $$ = arrayTable[$1][(int )$3];
          }
      }
    ;
%%
int main(void){
    yyparse();
}
void yyerror(char const *msg) {
    fprintf(stderr, "error: %s\n", msg);
}