int a = 5;
cout << "a=" << a << endl;
// & 取地址符，用来取出变量的地址 
cout << "变量a的地址是："  << &a << endl;

int* p;
p = &a; 
cout << "p的值是：" << p << endl ;

int b = 6;
p = &b;

cout << *p << endl; //*p，就找到他指向变量的值 
*p = 7;
cout << b << endl;