阅读下列程序，写出运行结果： #include

#include<iostream>
using namespace std;
class A
{
public :
A() { a = 5; }
void printa() { cout << "A:a = " << a << endl; }
private :
int a;
friend  class B;
};
class B
{
public:
void display1( A t )
{ t.a ++; cout << "display1:a = " << t.a << endl; };
void display2( A t )
{ t.a --; cout << "display2:a = " << t.a << endl; };
};
int main()
{
A obj1;
B obj2;
obj1.printa();
obj2.display1( obj1 );
obj2.display2( obj1 );
obj1.printa();
}