《C++游戏编程入门》第5章 函数:Mad Lib

5.1 创建函数

Standard Template Library，提供算法、容器和迭代器等。

05.instructions.cpp

#include <iostream>
using namespace std;

// 函数原型 (声明，调用前)
void instructions();

int main()
{
    instructions();//函数调用

    return 0;
}

// 函数定义
void instructions()//函数头部
{//函数体
    cout << "Welcome to the most fun you've ever had with text!\n\n";
    cout << "Here's how to play the game...\n";
}

5.2 使用形参和返回值

05.yes_or_no.cpp

#include <iostream>
#include <string>
using namespace std;

char askYesNo1();                // 指定返回类型char
char askYesNo2(string question); // 指定参数string类型

int main()
{
    char answer1 = askYesNo1(); // 使用返回值
    cout << "Thanks for answering: " << answer1 << "\n\n";

    char answer2 = askYesNo2("Do you wish to save your game?"); // 形参传值
    cout << "Thanks for answering: " << answer2 << "\n";

    return 0;
}

char askYesNo1()
{
    char response1;
    do
    {
        cout << "Please enter 'y' or 'n': ";
        cin >> response1;
    } while (response1 != 'y' && response1 != 'n');

    return response1; // return返回值
}

// 封装，隐藏细节，分开独立代码
char askYesNo2(string question)
{
    char response2;
    do
    {
        cout << question << " (y/n): "; // 使用形参
        cin >> response2;
    } while (response2 != 'y' && response2 != 'n');

    return response2;
}

5.4 使用作用域

变量作用域决定可见范围。

05.scoping.cpp

#include <iostream>
using namespace std;

void func();

int main()
{
    int var = 5; // local variable in main()
    cout << "In main() var is: " << var << "\n\n";

    func();

    cout << "Back in main() var is: " << var << "\n\n";

    { // 嵌套作用域
        cout << "In main() in a new scope var is: " << var << "\n\n";

        cout << "Creating new var in new scope.\n";
        int var = 10; // variable in new scope, hides other variable named var
        cout << "In main() in a new scope var is: " << var << "\n\n";
    }

    cout << "At end of main() var created in new scope no longer exists.\n";
    cout << "At end of main() var is: " << var << "\n";

    for (int i = 0; i < 3; i++) // 循环外不存在
        cout << i << endl;

    return 0;
}

void func()
{
    int var = -5; // 局部变量，函数外不可见
    cout << "In func() var is: " << var << "\n\n";
}

5.5 使用全局变量

全局变量，程序各部分间共享信息（任意部分都能访问的变量）。
尽量少用。

05.global_reach.cpp

#include <iostream>
using namespace std;

int glob = 10; // 全局变量定义并初始化
void access_global();
void hide_global();
void change_global();

int main()
{
    cout << "In main() glob is: " << glob << "\n\n"; // 访问全局变量
    access_global();

    hide_global();
    cout << "In main() glob is: " << glob << "\n\n";

    change_global();
    cout << "In main() glob is: " << glob << "\n\n";

    return 0;
}

void access_global()
{
    cout << "In access_global() glob is: " << glob << "\n\n"; // 访问全局变量
}

void hide_global()
{
    int glob = 0; // 隐藏全局变量
    cout << "In hide_global() glob is: " << glob << "\n\n";
}

void change_global()
{
    glob = -10; // 改变全局变量
    cout << "In change_global() glob is: " << glob << "\n\n";
}

5.7 使用默认参数

为函数形参指定默认值。

05.give_me_a_number.cpp

#include <iostream>
#include <string>
using namespace std;

int askNumber(int high, int low = 1); // 函数声明中指定默认参数，默认参数放在最后面

int main()
{
    int number = askNumber(5);
    cout << "Thanks for entering: " << number << "\n\n";

    number = askNumber(10, 5);
    cout << "Thanks for entering: " << number << "\n\n";

    return 0;
}

int askNumber(int high, int low)
{
    int num;
    do
    {
        cout << "Please enter a number"
             << " (" << low << " - " << high << "): ";
        cin >> num;
    } while (num > high || num < low);

    return num;
}

5.8 函数重载

函数名相同，形参个数或类型不相同。

05.triple.cpp

#include <iostream>
#include <string>
using namespace std;

int triple(int number);
string triple(string text);

int main()
{
    cout << "Tripling 5: " << triple(5) << "\n\n";
    cout << "Tripling 'gamer': " << triple("gamer");

    return 0;
}

int triple(int number)
{
    return (number * 3);
}

string triple(string text)
{
    return (text + text + text);
}

5.9 内联函数

短小函数，直接复制到调用处，程序不必跳转。

05.taking_damage.cpp

#include <iostream>
using namespace std;

int radiation(int health);//函数声明中不能使用inline

int main()
{
    int health = 80;
    cout << "Your health is " << health << "\n\n";

    health = radiation(health);
    cout << "After radiation exposure your health is " << health << "\n\n";

    health = radiation(health);
    cout << "After radiation exposure your health is " << health << "\n\n";

    health = radiation(health);
    cout << "After radiation exposure your health is " << health << "\n\n";

    return 0;
}

inline int radiation(int health)
{
    return (health / 2);
}

5.10 Mad Lib游戏

05.mad-lib.cpp

#include <iostream>
#include <string>
using namespace std;

string askText(string prompt);
int askNumber(string prompt);
void tellStory(string name, string noun, int number, string bodyPart, string verb);

int main()
{
    cout << "Welcome to Mad Lib.\n\n";
    cout << "Answer the following questions to help create a new story.\n";

    string name = askText("Please enter a name: ");
    string noun = askText("Please enter a plural noun: ");
    int number = askNumber("Please enter a number: ");
    string bodyPart = askText("Please enter a body part: ");
    string verb = askText("Please enter a verb: ");

    tellStory(name, noun, number, bodyPart, verb);

    return 0;
}

string askText(string prompt)
{
    string text;
    cout << prompt;
    cin >> text;
    return text;
}

int askNumber(string prompt)
{
    int num;
    cout << prompt;
    cin >> num;
    return num;
}

void tellStory(string name, string noun, int number, string bodyPart, string verb)
{
    cout << "\nHere's your story:\n";
    cout << "The famous explorer ";
    cout << name;
    cout << " had nearly given up a life-long quest to find\n";
    cout << "The Lost City of ";
    cout << noun;
    cout << " when one day, the ";
    cout << noun;
    cout << " found the explorer.\n";
    cout << "Surrounded by ";
    cout << number;
    cout << " " << noun;
    cout << ", a tear came to ";
    cout << name << "'s ";
    cout << bodyPart << ".\n";
    cout << "After all this time, the quest was finally over. ";
    cout << "And then, the ";
    cout << noun << "\n";
    cout << "promptly devoured ";
    cout << name << ". ";
    cout << "The moral of the story? Be careful what you ";
    cout << verb;
    cout << " for.";
}