notes of C++

1* using namespace std;
    had better used in .cpp file but not in .h file
     namespace like a space which can contain class/variable/function and so on
     1)create a namespace
          namespace demo{
               int i,j;
                content....
          }
     2)use a namespace which exists in below two ways
          (1)
            using namespace demo
            void test()
            {
                 cout<            }   
          (2)
            void test()
            {
                cout<            }
2* head file standard
    #ifndef  _XXX_H_
    #define _XXX_H_
    ...some declaration
    #endif

3* ram leakage And ram patch
    ram leakage: because don't free() after malloc() , or don't delete() after new()
        :error operate and must be  avoid
    ram patch: because frequently free() and malloc() or delete() and new()
        :normal but must be consider

4* transmit parameter
    1)by value
        like: int a; b(a); //b() is a function use a as one formal parameter
            the value of a's change in b() will not affect the value of a out of b();  
    2) by quote
        like : void b(int &temp);
                int a;b(a);//the change of a in b() will affect the value of a out of b().
    3)by pointer
        like : void b(int * temp);
                int a;b(&a);//the change of a in b() will affect the value of a out of b().