Elementary

Basic Ideas

• object-oriented | 物件导向-面向对象

An object, or entity(either visible or invisible), is a variable in programming languages, made up of two primary components:

• Attibutes, or Data, representing the object's properties and status
• Services, or Operations, refered to as functions in programming.

C++ Focuses on things instead of operations.

Key words

• interface
• communications
• protection
• the hidden implementation
• encapsulation

OOP characteristics

• Everything is an object.
• A program is a bunch of objects telling each other what to do/(not how to do) by sending messages
• Each object has its own memory made up of other objects.
• Every object has a type.
• All objects of a particular type can receive the same messages. (Using the method to distinguish between different types or classes)

Header Files

To prevent defining repeatedly:

x.h

# pragma once //只包含这个头文件一次

or the same as C language:

log.h

# ifndef _LOG_H
# define _LOG_H
//...//
# endif

declaration

• external variables
• function prototypes
• class/struct declarations

:: resolver

::

<Class Name>::<function name>//not free
::<function name>

void S::f(){
  ::f();//would be recursive otherwise
  ::a++;//select the global a
  a—;//select the partial a
}

String

C++

#include<string>
String age, name; 
cin >> age >> name;
cout << name; 

• A class type, not a primitive type.
• Initially name is all zero. No matter it is static or global.
• No \0 at the end of the string.

Reference

Reference make use of the idea of a pointer, but is used as a normal variable rather than pointer. It is widely used in passing variables into a function.

C++

char c;
char & r = c;// a reference to c;

Some notes on reference:

• cannot be NULL.
• cannot calculate.
• No reference to reference

C++

int &* r; // No pointer to reference 
int *& r; // We have reference to pointer