C++学習の道(3):関数にオブジェクトを渡す

//        
#include <iostream>
using namespace std;
class aClass
{
   public:
       aClass(int n)
       { i = n; }
       void set(int n)
       { i = n; }
       int get()
       { return i; }
   private:
       int i;
};
//          (  )
void sqr1(aClass ob)
{
    ob.set(ob.get()*ob.get());
    cout<<"Copy of obj has i value of ";
    cout<<ob.get()<<endl;
}
//            (  )
void sqr2(aClass *ob)
{
    ob->set(ob->get()*ob->get());
    cout<<"Copy of obj has i value of ";
    cout<<ob->get()<<endl;
}
//             
void sqr3(aClass &ob)
{
    ob.set(ob.get()*ob.get());
    cout<<"Copy of obj has i value of ";
    cout<<ob.get()<<endl;
}

int main()
{
    aClass obj(10);

    cout<<"----        ----"<<endl;
    sqr1(obj);
    cout<<"But, obj.i is unchanged in main:";
    cout<<obj.get()<<endl;

    cout<<"----          ----"<<endl;
    sqr2(&obj);
    cout<<"Now, obj.i in main() has been changed. :";
    cout<<obj.get()<<endl;

    cout<<"----           ----"<<endl;
    //         obj     i  ，    。 
    obj.set(10); 

    sqr3(obj);
    cout<<"Now, obj.i in main() has been changed. :";
    cout<<obj.get()<<endl;

    return 0;
}