TC++PL上的计算器代码

TC++PL上的计算器代码(3)                   }
                 return error("divide by 0");
        default:
                return left;
        }
}
double expr(bool get)       //加和减
{
      double left=term(get);
          for(;;)
            switch(curr_tok){
            case PLUS:
                  left+=term(true);
                  break;
            case MINUS:
                  left-=term(true);
                 break;
            default:
                return left;
            }
}
int main()
{
   table["pi"]=3.1415926535897932385;
   table["e"]=2.7182818284590452354;
   while(cin){
       get_token();
       if(curr_tok==END)break;
       if(curr_tok==PRINT)continue;
       cout<<expr(false)<<"\n";