设置好内部状态，然后根据不同的函数作为行为模式，进行状态转换。

有点像Finite Automata算法，两者的思想是一样的。

会Finite Automata，那么这个设计模式就很容易了。

#pragma once
#include <stdlib.h>
#include <math.h>
#include <random>
#include <time.h>

enum STATES
{
	FULLY_RENTED, WAITING, GOT_APPLICATION, APARTMENT_RENTED
};

class RentalMethods
{
	STATES state;
	int numberOfAppartments;
public:
	RentalMethods(int n):state(WAITING), numberOfAppartments(n)
	{
		srand((unsigned)time(NULL));
	}
	void getApplication()
	{
		switch (state)
		{
		case FULLY_RENTED:
			puts("Sorry, we are fully rented.");
			break;
		case WAITING:
			state = GOT_APPLICATION;
			puts("Thanks for the application.");
			break;
		case GOT_APPLICATION:
			puts("We already got your application.");
			break;
		case APARTMENT_RENTED:
			puts("Hang on, we are renting you an apartment.");
			break;
		}
	}

	void checkApplication()
	{
		bool yesOrNo = rand() % 2;

		switch (state)
		{
		case FULLY_RENTED:
			puts("Sorry, we are fully rented.");
			break;
		case WAITING:
			puts("You have to submit an application.");
			break;
		case GOT_APPLICATION:
			{
				if (yesOrNo && numberOfAppartments > 0)
				{
					puts("Congratulations, you were approved.");
					state = APARTMENT_RENTED;
					rentApartment();
				}
				else
				{
					puts("Sorry, you were not approved.");
					state = WAITING;
				}
			}
			break;
		case APARTMENT_RENTED:
			puts("Hang on, we are renting you an apartment.");
			break;
		}
	}

	void rentApartment()
	{
		switch (state)
		{
		case FULLY_RENTED:
			puts("Sorry, we are fully rented.");
			break;
		case WAITING:
			puts("You have to submit an application.");
			break;
		case GOT_APPLICATION:
			puts("You must have your application checked.");
			break;
		case APARTMENT_RENTED:
			puts("Renting you an apartment...");
			numberOfAppartments--;
			dispenseKeys();
			break;
		}
	}

	void dispenseKeys()
	{
		switch (state)
		{
		case FULLY_RENTED:
			puts("Sorry, we are fully rented.");
			break;
		case WAITING:
			puts("You have to submit an application.");
			break;
		case GOT_APPLICATION:
			puts("You must have your application checked.");
			break;
		case APARTMENT_RENTED:
			puts("Here are your key!");
			state = WAITING;
			break;
		}
	}
};

void States_Run()
{
	RentalMethods rentalMethods(9);

	rentalMethods.getApplication();
	rentalMethods.checkApplication();
}

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