#include<iostream>
#include<map>
using namespace std;

class Command{
public:
 virtual void Invoke(int*,int)=0;
};
class CmdPlus :public Command{
 CmdPlus(){};
 void Invoke(int* agNum1,int agNum2){
  *agNum1+=agNum2;
 }
 friend class CmdManager;
};
class CmdMinus:public Command{
 CmdMinus(){}
 void Invoke(int* agNum1,int agNum2){
  *agNum1-=agNum2;
 }
 
 friend class CmdManager;
};
class CmdManager{
 static CmdManager* cm;
 int mAnswer;
 map<char, Command*> mArrayofCmd;
 void lnit(){
  mAnswer=0;
  AddCmd();
 }
 void AddCmd(){
  mArrayofCmd['+']=new CmdPlus();
  mArrayofCmd['-']=new CmdMinus();
 }
public:
 static CmdManager * getInstance(){
  if(cm==NULL){
   CmdManager* instanceOfCM=new CmdManager();
   instanceOfCM->lnit();
   return instanceOfCM;
  }
  return cm;
 }
 static void destroyInstance(){
  if(cm!=NULL){
   delete cm;
  }
 }
 void Invoke(int agNum,char agOperator){
  mArrayofCmd[agOperator]->Invoke(&mAnswer,agNum);
 }
 int getAnswer(){
  return mAnswer;
 }
};
CmdManager* CmdManager::cm=NULL;
int main(){
 CmdManager* cm=CmdManager::getInstance();
 cm->Invoke(5,'+');
 cm->Invoke(3,'+');
 cm->Invoke(2,'-');
 cout<<"Answer = "<<cm->getAnswer()<<endl;
 CmdManager::destroyInstance();
}

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순수가상함수 Invoke를 재정의하여 각 클래스에 맞게 연산하도록 하였다.

CmdManager클래스를 이용해 각각의 연산을 분류해서 호출하고 각 연산의 값을 누적시켰다.