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

(C++ の初歩： 構造体 + 関数 = クラス)

Computing Practice I

8th lecture, May 31, 2018

http://www.sw.it.aoyama.ac.jp/2018/CP1/lecture8.html

Martin J. Dürst

© 2005-18 Martin J. Dürst 青山学院大学

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

07C2/C3: Reuse functions in other functions!

Environment for C++ Exercises

• File extension: .c → .cpp (also: .C, .cc, .CPP, .c++, .cp, .cxx)
• 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)

Member Functions: Important

• 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: 1st argument of a function → 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: 複素数のクラスの作成
• 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

インデントについて: public:/private: は普通のインデントの半分

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