171014 C++学习笔记-4

例 4-1 时钟类的完整程序

// ConsoleApplication1.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>  
using namespace std;

//Part One：定义类
class Clock {
public:
    void setTime(int newH = 0, int newM = 0, int newS = 0);
    void showTime();
private:
    int hour, minute, second;
};

//Part Two：成员函数的实现
void Clock::setTime(int newH, int newM, int newS) {
    hour = newH;
    minute = newM;
    second = newS;
}

inline void Clock::showTime() {
    cout << hour << ":" << minute << ":" << second << endl;
}

//Part Three：主函数
int main() {
    Clock myClock;
    cout << "First time set and output:" << endl;
    myClock.setTime();
    myClock.showTime();
    cout << "Second time set and output:" << endl;
    myClock.setTime(8, 30, 30);
    myClock.showTime();
    return 0;
}

例 4-2 Point类的完整程序

// ConsoleApplication2.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
using namespace std;

class Point {
public:
    Point(int xx = 0, int yy = 0) { //内联函数
        x = xx;
        y = yy;
    }
    Point(Point &p);               // 复制构造函数
    int getX() {
        return x;
    }
    int getY() {
        return y;
        }
private:
    int x, y;
};

//成员函数的实现，复制构造函数
Point::Point(Point &p) {
    x = p.x;
    y = p.y;
    cout << "Calling the copy constructor" << endl;
}

// 形参为Poin类对象的函数
void fun1(Point p) {
    cout << p.getX() << endl;
}
// 返回值为Point类对象的函数
Point fun2() {
    Point a(1, 2);
    return a;
}
int main()
{
    Point a(4, 5);              //第一个对象a
    Point b = a;                //情况一，用a初始化b。第一次调用复制构造函数
    cout << b.getX() << endl;   
    fun1(b);                    //情况二，对象b作为fun1的实参。第二次调用复制函数
    b = fun2();                 //情况三，函数的返回值是类对象，函数返回时，调用复制构造函数
    cout << b.getX() << endl;
    return 0;
}

例 4-3 游泳池改造预算，Circle类

// ConsoleApplication2.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <iostream>
using namespace std;

const float PI = 3.141593;          //给出PI的值
const float FENCE_PRICE = 35;       //栅栏的单价
const float CONCRETE_PRICE = 20;    //过道水泥单价

class Circle {                      //声明定义类Circle及其数据和方法
public:                             //外部接口
    Circle(float r);                //构造函数
    float circumference();          //计算圆的周长
    float area();                   //计算圆的面积
private:                            //私有数据成员
    float radius;                   //圆半径
    };
Circle::Circle(float r) {
    radius = r;
}
// 等价于：Circle::Circle(float r):radius(r){} --->列表表达式，效率更高

//计算圆的周长
float Circle::circumference() {
    return 2 * PI*radius;
}

//计算圆环的面积
float Circle::area() {
    return PI*radius*radius;
}

int main()
{
    float radius;
    cout << "Enter the radius of the pool:";//提示用户输入半径
    cin >> radius;
    Circle pool(radius);                    //游泳池边界对象
    Circle poolRim(radius + 3);             //栅栏对象
    //计算栅栏造价并输出
    float fenseCost = poolRim.circumference()*FENCE_PRICE;
    cout << "Fencing Cost is $ " << fenseCost << endl;

    //计算过道造价并输出
    float concreCost = (poolRim.area() - pool.area())*CONCRETE_PRICE;
    cout << "Concrete Cost is $ " << concreCost << endl;

    return 0;
}

例 4-4 类的组合，线段(Line)类

// ConsoleApplication1.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>  
#include<cmath>
using namespace std;

class Point {   //Point类的定义
public:
    //构造函数，隐式申明
    Point(int xx = 0, int yy = 0) {
        x = xx;
        y = yy;
    }
    //复制构造函数
    Point(Point &p);
    //内联成员函数，隐式声明；
    int getX() { return x; }
    int getY() { return y; }
private:
    int x, y;
};

//复制构造函数的实现
Point::Point(Point &p) {
    x = p.x;
    y = p.y;
    cout << "Calling the copy constructor of Point" << endl;
}

//类的组合
class Line { //Line类的定义
public:      //外部接口
    Line(Point xp1, Point xp2); //构造函数，形参为Point类
    Line(Line &l);              //复制构造函数，内联成员函数
    double getLen() { return len; }
private:
    Point p1, p2;               //Point类的对象p1,p2
    double len;
};

//组合类的构造函数
Line::Line(Point xp1, Point xp2) : p1(xp1), p2(xp2) //初始化列表，奖形参xp1,xp2赋予p1,p2
{ 
    cout << "Calling constructor of Line" << endl;
    double x = static_cast<double>(p1.getX() - p2.getX());
    double y = static_cast<double>(p1.getY() - p2.getY());
    len = sqrt(x*x + y*y);                          //计算得到len，len仅能被Line类中的共有函数getLen()访问
}

//组合类的复制构造函数
Line::Line(Line &l) :p1(l.p1), p2(l.p2)             //l为对象名
{
    cout << "Calling the copy constructor of Line" << endl;
    len = l.len;
}

int main() {
    Point myp1(1, 1), myp2(4, 5);               //建立Point类的对象
    Line line(myp1, myp2);                      //建立Line类的对象
    Line line2(line);                           //利用复制构造函数建立一个新对象
    cout << "The length of the line is: ";
    cout << line.getLen() << endl;
    cout << "The length of the line2 is: ";
    cout << line2.getLen() << endl;
    return 0;
}

例 4-7 用结构体表示学生的基本信息

有时程序中需要定义一些数据类型，它们并没有什么操作，定义它们的目的只是将一些不同类型的数据组合成一个整体，从而方便地保存数据，这样的类型不妨定义为结构体。

// ConsoleApplication1.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>  
//#include<iomanip> 流控制符：1.设置显示宽度 2.设置左右对齐 3.设置浮点数精度
#include<string>
using namespace std;

struct Student {
    int num;
    string name;
    char sex;
    int age;
};


int main() {
    Student stu = { 97001,"Lin Lin",'F',19 };
    cout << "Num: " << stu.num << endl;
    cout << "Name: " << stu.name << endl;
    cout << "Sex: " << stu.sex << endl;
    cout << "Age: " << stu.age << endl;
    return 0;
}

例 4-8 使用联合体保存成绩信息，并且输出

// ConsoleApplication1.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>  
#include<string>
using namespace std;

class ExamInfo {
public:
    //3种构造函数，分别用登记、是否通过和百分制来初始化
    ExamInfo(string name, char grade)
        :name(name), mode(GRADE), grade(grade) {}
    ExamInfo(string name, bool pass)
        :name(name), mode(PASS), pass(pass) {}
    ExamInfo(string name, int percent)
        :name(name), mode(PERCENTAGE), percent(percent) {}
    void show();

private:
    string name;        //课程名称
    enum {
        GRADE,
        PASS,
        PERCENTAGE
    }mode;              //采用何种计分方式,此处为何是这样的写法？？？
    union {
        char grade;     //等级制的成绩
        bool pass;      //是否通过
        int percent;    //百分制的成绩
    };
};

void ExamInfo::show() //成员函数
{
    cout << name<<": ";

    switch (mode) {
    case GRADE: cout << grade;
        break;
    case PASS:
        cout << (pass ? "PASS" : "FAIL");
        break;
    case PERCENTAGE:
        cout << percent;
        break;
    }
    cout << endl;
}

int main() {
    ExamInfo course1("English", 'B');
    ExamInfo course2("Calculus", true);
    ExamInfo course3("C++Programming", 85);
    course1.show();
    course2.show();
    course3.show();
    return 0;
}

例 4-9 个人银行账户管理程序

// ConsoleApplication1.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include<iostream>  
#include<string>
#include <cmath>
using namespace std;

class SavingsAccount {      //存储账户类
private:
    int id;                 //账号ID
    double balance;         //余额
    double rate;            //存款的年利率
    int lastDate;           //上次变更余额的时间
    double accumulation;        //余额按日累加之和

    //记录一笔账，date为日期，amount为金额，desc为说明
    void record(int date, double amount);
    //获得指定日期为止的存款金额按日累加值
    double accumulate(int date) const{
        return accumulation + balance*(date - lastDate);
    }
public:
    //构造函数
    SavingsAccount(int date, int id, double rate);
    int getId() { return id; }
    double getBalance() { return balance; }
    double getRate() { return rate; }
    void deposit(int date, double amount);      //存入现金
    void withdraw(int date, double amount);     //取出现金
    //结算利息，每年1月1日调用一次该函数
    void settle(int date);
    //显示账户信息
    void show();
};

//SavingsAccount 类相关成员函数的实现
//-1 构造函数，初始化对象
SavingsAccount::SavingsAccount(int date, int id, double rate)
    :id(id), balance(0), rate(rate), lastDate(date), accumulation(0) {
    cout << date << "\t#" << id << " is created" << endl;
}

//-2 
void SavingsAccount::record(int date, double amount) {
    accumulation = accumulate(date);
    lastDate = date;
    amount = floor(amount * 100 + 0.5) / 100;
    balance += amount;
    cout << date << "\t#" << id << "\t" << amount << "\t" << balance << endl;
}

//-3 
void SavingsAccount::deposit(int date, double amount) { 
    record(date, amount); }


//-4 
void SavingsAccount::withdraw(int date, double amount) {
    if (amount > getBalance())
        cout << "Error: not enough money" << endl;
    else
        record(date, -amount);
}
//-5
void SavingsAccount::settle(int date) {
    double interest = accumulate(date)*rate / 365;
    if (interest != 0)
        record(date, interest);
    accumulation = 0;
}
//-6
void SavingsAccount::show() {
    cout << "#" << id << "\tBalance: " << balance;
}

int main() {
    //建立几个账号
    SavingsAccount sa0(1, 21325302, 0.015);
    SavingsAccount sa1(1, 58320212, 0.015);
    //几笔账目
    sa0.deposit(5, 5000);
    sa1.deposit(25, 10000);
    sa0.deposit(45, 5500);
    sa1.withdraw(60, 4000);
    //开户后第90天到了银行的计息日，结算所有账户的年息
    sa0.settle(90);
    sa1.settle(90);
    //输出各个账户的信息
    sa0.show(); cout << endl;
    sa1.show(); cout << endl;
    return 0;
}