C++代码编写：1.编写一个Date类，有checkMonth和checkDay函数以检查月份和日期的合法性，有判断是否为闰年的函数，设计定义set类函数，用以设定年，月份和日期，设计定义多个get函数用以获取年、月和日。 2. 创建一个抽象类employee类，该类中有姓名（sting 类型），ID（sting 类型）和出生日期(Date类型)。定义构造函数初始化每个成员；定义changeName()函数用来修改姓名，定义Display()函数用来显示每个员工的基本信息。纯虚函数为发放工资函数。 3.创建由Employee类派生出的其它四个员工类Salaried Employee,Commission Employee，Hourly Employee,以及由Commission Employee派生出的BasePlus Commission Employee。编写他们的新增成员、构造函数等，他们都有一个计算工资的函数。

1. Date类的代码如下：

class Date {
private:
    int year;
    int month;
    int day;
    bool isLeapYear() {
        return (year % 4 == 0 && year % 100 != 0) || year % 400 == 0;
    }
public:
    Date(int y = 0, int m = 0, int d = 0) {
        year = y;
        month = m;
        day = d;
    }
    bool checkMonth() {
        return month >= 1 && month <= 12;
    }
    bool checkDay() {
        if (month == 2) {
            if (isLeapYear()) {
                return day >= 1 && day <= 29;
            } else {
                return day >= 1 && day <= 28;
            }
        } else if (month == 4 || month == 6 || month == 9 || month == 11) {
            return day >= 1 && day <= 30;
        } else {
            return day >= 1 && day <= 31;
        }
    }
    void setYear(int y) {
        year = y;
    }
    void setMonth(int m) {
        month = m;
    }
    void setDay(int d) {
        day = d;
    }
    int getYear() {
        return year;
    }
    int getMonth() {
        return month;
    }
    int getDay() {
        return day;
    }
};

2. Employee类的代码如下：

class Employee {
private:
    string name;
    string id;
    Date birthDate;
public:
    Employee(string n, string i, Date bd) {
        name = n;
        id = i;
        birthDate = bd;
    }
    void changeName(string n) {
        name = n;
    }
    void Display() {
        cout << "Name: " << name << endl;
        cout << "ID: " << id << endl;
        cout << "Birth Date: " << birthDate.getYear() << "-" << birthDate.getMonth() << "-" << birthDate.getDay() << endl;
    }
    virtual double pay() = 0;
};

注意到这里声明了一个纯虚函数pay()，表示需要在派生出的具体类中实现。

3. SalariedEmployee类、CommissionEmployee类、HourlyEmployee类和BasePlusCommissionEmployee类的代码如下：

class SalariedEmployee : public Employee {
private:
    double salary;
public:
    SalariedEmployee(string n, string i, Date bd, double s) : Employee(n, i, bd) {
        salary = s;
    }
    double pay() {
        return salary;
    }
};

class CommissionEmployee : public Employee {
private:
    double sales;
    double rate;
public:
    CommissionEmployee(string n, string i, Date bd, double s, double r) : Employee(n, i, bd) {
        sales = s;
        rate = r;
    }
    double pay() {
        return sales * rate;
    }
};

class HourlyEmployee : public Employee {
private:
    double wage;
    double hours;
public:
    HourlyEmployee(string n, string i, Date bd, double w, double h) : Employee(n, i, bd) {
        wage = w;
        hours = h;
    }
    double pay() {
        if (hours <= 40) {
            return wage * hours;
        } else {
            return wage * 40 + wage * 1.5 * (hours - 40);
        }
    }
};

class BasePlusCommissionEmployee : public CommissionEmployee {
private:
    double baseSalary;
public:
    BasePlusCommissionEmployee(string n, string i, Date bd, double s, double r, double b) : CommissionEmployee(n, i, bd, s, r) {
        baseSalary = b;
    }
    double pay() {
        return CommissionEmployee::pay() + baseSalary;
    }
};

这里可以看到，派生类的构造函数中都直接调用了基类的构造函数，使用了冒号“:”语法。同时，派生类中的pay()函数都实现了基类中声明的纯虚函数。