《C++游戏编程入门》第8章 类：Critter Caretaker
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- [8.1 定义新类型](#8.1 定义新类型)
- [8.2 使用构造函数](#8.2 使用构造函数)
- [8.3 设置成员访问级别](#8.3 设置成员访问级别)
- [8.4 使用静态数据成员与静态成员函数](#8.4 使用静态数据成员与静态成员函数)
- [8.5 Critter Caretaker游戏](#8.5 Critter Caretaker游戏)
8.1 定义新类型
08.simple_critter.cpp
cpp
#include <iostream>
using namespace std;
class Critter // 类定义，定义新类型Critter
{
public:
int m_Hunger; // 声明数据成员
void Greet(); // 声明成员函数
};
void Critter::Greet() // 成员函数定义
{
cout << "Hi. I'm a critter. My hunger level is " << m_Hunger << ".\n";
}
int main()
{
Critter crit1; // 对象实例化
Critter crit2;
crit1.m_Hunger = 9; // 对象操作
cout << "crit1's hunger level is " << crit1.m_Hunger << ".\n";
crit2.m_Hunger = 3;
cout << "crit2's hunger level is " << crit2.m_Hunger << ".\n\n";
crit1.Greet(); // 成员函数调用
crit2.Greet();
return 0;
}8.2 使用构造函数
构造函数，实例化新对象时自动调用，通常初始化工作，给数据成员赋值。
08.constructor_critter.cpp
cpp
#include <iostream>
using namespace std;
class Critter
{
public:
int m_Hunger;
Critter(int hunger = 0); // 声明构造函数，提供默认参数
void Greet();
};
Critter::Critter(int hunger) // 定义构造函数
{
cout << "A new critter has been born!" << endl;
m_Hunger = hunger;
}
void Critter::Greet()
{
cout << "Hi. I'm a critter. My hunger level is " << m_Hunger << ".\n\n";
}
int main()
{
Critter crit(7);
crit.Greet();
return 0;
}8.3 设置成员访问级别
避免直接修改或访问对象的数据成员，让成员函数维护。
08.private_critter.cpp
cpp
#include <iostream>
using namespace std;
class Critter
{
public: // begin public section
Critter(int hunger = 0);
int GetHunger() const;
void SetHunger(int hunger);
private: // begin private section
int m_Hunger;
};
Critter::Critter(int hunger)
: m_Hunger(hunger)
{
cout << "A new critter has been born!" << endl;
}
int Critter::GetHunger() const // const不能修改非静态数据成员值，不能调用非常量成员函数
{
return m_Hunger;
}
void Critter::SetHunger(int hunger)
{
if (hunger < 0)
{
cout << "You can't set a critter's hunger to a negative number.\n\n";
}
else
{
m_Hunger = hunger;
}
}
int main()
{
Critter crit(5);
// cout << crit.m_Hunger; -- illegal, m_Hunger is private!
cout << "Calling GetHunger(): " << crit.GetHunger() << "\n\n";
cout << "Calling SetHunger() with -1.\n";
crit.SetHunger(-1);
cout << "Calling SetHunger() with 9.\n";
crit.SetHunger(9);
cout << "Calling GetHunger(): " << crit.GetHunger() << "\n\n";
return 0;
}8.4 使用静态数据成员与静态成员函数
08.static_critter.cpp
cpp
#include <iostream>
using namespace std;
class Critter
{
public:
static int s_Total; // 静态成员变量声明
// total number of Critter objects in existence
Critter(int hunger = 0);
static int GetTotal(); // 静态成员函数声明
private:
int m_Hunger;
};
int Critter::s_Total = 0; // 静态成员变量定义并初始化
Critter::Critter(int hunger) : m_Hunger(hunger)
{
cout << "A critter has been born!" << endl;
++s_Total;
}
int Critter::GetTotal() // 静态成员函数定义，不能访问非静态数据成员
{
return s_Total;
}
int main()
{
cout << "The total number of critters is: ";
cout << Critter::s_Total << "\n\n"; // 访问静态常用变量
Critter crit1, crit2, crit3;
cout << "\nThe total number of critters is: ";
cout << Critter::GetTotal() << "\n"; // 调用静态成员函数
return 0;
}8.5 Critter Caretaker游戏
08.critter_caretaker.cpp
cpp
#include <iostream>
using namespace std;
class Critter
{
public:
Critter(int hunger = 0, int boredom = 0);
void Talk();
void Eat(int food = 4);
void Play(int fun = 4);
private:
int m_Hunger; // 饥饿程度
int m_Boredom; // 厌倦程度
int GetMood() const;
void PassTime(int time = 1);
};
Critter::Critter(int hunger, int boredom)
: m_Hunger(hunger), m_Boredom(boredom)
{
}
inline int Critter::GetMood() const
{
return (m_Hunger + m_Boredom);
}
void Critter::PassTime(int time)
{
m_Hunger += time;
m_Boredom += time;
}
void Critter::Talk()
{
cout << "I'm a critter and I feel ";
int mood = GetMood();
if (mood > 15)
cout << "mad.\n";
else if (mood > 10)
cout << "frustrated.\n";
else if (mood > 5)
cout << "okay.\n";
else
cout << "happy.\n";
PassTime();
}
void Critter::Eat(int food)
{
cout << "Brruppp.\n";
m_Hunger -= food;
if (m_Hunger < 0)
m_Hunger = 0;
PassTime();
}
void Critter::Play(int fun)
{
cout << "Wheee!\n";
m_Boredom -= fun;
if (m_Boredom < 0)
m_Boredom = 0;
PassTime();
}
int main()
{
Critter crit;
crit.Talk();
int choice;
do
{
cout << "\nCritter Caretaker\n\n";
cout << "0 - Quit\n";
cout << "1 - Listen to your critter\n";
cout << "2 - Feed your critter\n";
cout << "3 - Play with your critter\n\n";
cout << "Choice: ";
cin >> choice;
switch (choice)
{
case 0:
cout << "Good-bye.\n";
break;
case 1:
crit.Talk();
break;
case 2:
crit.Eat();
break;
case 3:
crit.Play();
break;
default:
cout << "\nSorry, but " << choice << " isn't a valid choice.\n";
}
} while (choice != 0);
return 0;
}