First steps towards C++:
Structures + Functions = Classes

(C++ の初歩：構造体 + 関数 = クラス)

Computing Practice I

8th lecture, June 8, 2017

http://www.sw.it.aoyama.ac.jp/2017/CP1/lecture8.html

Martin J. Dürst

Today's Schedule

Minitest
About last week's exercises
Object-orientation and C++
Today's exercises

ミニテスト

授業開始までにログイン済み
ナビゲーションは左に畳み、ブラウザは全画面に拡大
授業開始まで教科書、資料、筆箱、財布などを鞄に入れ、鞄を椅子の下に
テスト終了後その場で待つ

Results of Previous Exercises

	07A1	07B1	07C1	07C2	07C3
100 points	42	40	16	10	3
60 points	55	55	76	74	43
partial	-	-	-	-	17
errors	1	2	4	6	20
not submitted	1	2	3	9	16

07C3: Reuse functions in other functions!

Environment for C++ Exercises

File extension: .c → .cpp
Compiler: gcc → g++
(if necessary, use cygwin's setup.exe to add gcc-g++ on your home/notebook PC)
Use C input/output functions (#include <stdio.h>, printf, scanf,...)
Rest of environment is the same as for C exercises

C++ Overview

Fix 'mistakes' in C
Example 1: // comment until end of line
(later added to C, too)
Example 2: typedef struct {...} Person; → struct Person {...};
Add object-orientation to C
classes, member functions,...

Applications of C++: Browsers

Famous open-source browsers are written in C++
- Firefox (Mozilla)
- Webkit (Chrome, Safari, Opera,...)
Object-oriented languages are well suited for GUI programming
For low-level programming and high speed, C++ is best
Mozilla browser compressed source ca. 180MB

Purpose of Object-Orientation

(noun: object-orientation, adjective: object-oriented)

Combine data and operations
Encapsulate data, block inappropriate access and change
Most real-world programming languages use object-orientation in some way (the C/C++ is an exception)
Object-orientation becomes more and more useful as project size increases
Very important for large software projects

(not part of today's exercises:)

Inheritance
Polymorphism
...

Class Definition

class class_name {
    declarations of member variables
  public:
    declarations of constructors
    declarations of member functions
};

Example of Class Definition

class Point {
    double x, y;
  public:
    Point ();
    Point (double new_x, double new_y);
    void set_x (double new_x);
    void set_y (double new_y);
    double get_x ();
    double get_y ();
};

(set_... and get_... functions are called setter and getter and used to implement encapsulation)

Important Points for Member Functions

Declaration (inside class): Without class name
E.g.: void set_x (double new_x);
Definition (outside class): Class name is needed
E.g.: void Point::set_x (double new_x) { ... }
Use:
- Same as (structure) member variables
- Function, therefore () is necessary
- E.g.: Point p(2, 3); p.get_x();

Conversion from Function to Member Function

Function: Arguments and return value
Member function: Receiver, arguments, and return value
In most cases, a function's first argument is used as the receiver
As a result, there is one less argument
Example of call:
distance(start, end);
→start.distance(end);
Example of declaration:
double distance(Point start, Point end);
→ double distance(Point other);
Use of member (variables/functions) inside a member function:
Only the member name is used for members of the receiver
Example: x - other.x

Important Points for Constructors

Purpose: Create and initialize an instance
Same name as class name
No return value (void also not needed)
Possible to have multiple constructors with different (number or type of) arguments
Arguments are given after the variable name when a variable is defined
E.g.: Point p1(3.5, 7.4);
Constructor without arguments (default constructor):
- Automatically created if there are no other constructors
  (may still be needed to assure correct initialization)
- Declaration and definition necessary if there are other constructors

C++ Header Files

Extension is .h, same as for C
Definition of class (including declaration of constructors and member functions)
Definition (implementation) of constructors and member functions in .cpp file
Usually, one class per .h/.cpp pair, with class name identical to file name (Point.h and Point.cpp)

今日の演習

08A1: 以前作ったプログラムで struct を class に変更、public:/private: の体験
08A2: クラスを使って点の距離の計算
08B1: 日付のクラスの作成
08C1: 複素数クラスの作成
08C2: 温度クラスによる単位変換 (内部表現の隠蔽; 重要: 必須 (全員提出)、月曜締切)

08B1/08C1/08C2 ではメインプログラムを提出プログラムの最後に #include

次回までの準備

今日の復習
残りの演習問題を宿題として完成、提出
参考書の第 11 章 (pp. 282-311) をよく読む。
分かるところと分からないところをよく考える。

Glossary

object-orientation: オブジェクト指向
class: クラス
member function: メンバ関数
object-oriented (programming) language: オブジェクト思考 (プログラミング) 言語
encapsulation: カプセル化
inheritance: (クラスの) 継承
polymorphism: 多態性
member variables: メンバ変数
receiver: レシーバ
constructor: コンストラクタ
setter: セッタ
getter: ゲッタ

First steps towards C++: Structures + Functions = Classes