2022c++(Ⅱ)

选择

1. I in C++ , There is a kind of class that it can only be inherited but cannot be initiated, we call that class as a ( )，to define that kind of class, it has to have at least a ( ) 。(A) virtual function (B) pure virtual function (C) abstract class (D)friend class

根据题意，应选b：纯虚函数及c：抽象类。

一个包含纯虚函数的类无法创建对象，相应的将一个抽象类作为一个数据成员的类也无法创建对象。

1. Assume that AB is a class, the declaration of copy constructor of that class should be ( )。（A）AB&(AB x) (B)AB(AB x) (C)AB(AB &x) (D)AB(AB *x)

根据题意，应为c

用该类的对象创建另一个对象，即复制，需要传引用，防止在生成一堆数据浪费数据

1. For the member of a structure, the default access modifier is ( )。

   (A) public; (B) private; (C) protected; (D) static;

   根据题意，应为a

   类的默认属性使私有，而结构体默认属性是公有

2. Assume AB is a class, to execute statement “AB a(4),b[3],*p[2];”, how many times to invoke the constructor?( )。

   （A）3 (B) 4 (C) 6 (D) 9

   操作以左往右分别为，初始化的带参构造，默认构造的对象数组，未分配空间的指针数组

3. Which of the following is not correct ( )

   1. The name of constructor is same as the name of the class

   2. class constructor could have default parameters

   3. the default return type of a constructor is of type int

   4. the constructor can be overloaded

   构造函数不能return,也吗，没有指明返回类型

4. Parameterized stream manipulator setfill specifies the fill character that is displayed when an output is displayed in a field wider than the number of characters or digits in the output. The effect of setfill applies:

   1. Only to the current value being displayed.
   2. Only to outputs displayed in the current statement.
   3. Until explicitly set to a different setting.
   4. Until the output buffer is flushed.

std::setfill 是一个操纵符，它用于设置输出流的填充字符。当你需要在输出中对齐数据时，setfill 可以帮助你指定一个字符，当使用 setw 函数来设定输出宽度时，这个字符会被用来填充不足的部分。若字符超出了，则不会截断。

1. Assuming the following is the beginning of the constructor definition for class Circle which inherits from class Point,Circle::Circle( double r, int a, int b ) : Point( a, b ) The second line:

   1. Invokes the Point constructor with values a and b.
   2. Causes a compiler error.
   3. Is unnecessary because the Point constructor is called automatically.
   4. Indicates inheritance.

   用于给point中的可能私有数据成员赋值等操作，总之可用，不会报错

2. Which of the following assignments would be a compilation error?

   1) Assigning the address of a base-class object to a base-class pointer.
   2) Assigning the address of a base-class object to a derived-class pointer.
   3) Assigning the address of a derived-class object to a base-class pointer.
   4) Assigning the address of a derived-class object to a derived-class pointer.

   比如你能说狗是动物，但不能说动物是狗

3. Assume class T is declared as following，which of the following declaration of the function fF() is not correct( )。

class T

{ int i;

friend void fF(T&,int) ;

};

1) void fF (T &objT,int k) { objT.i = k+1; }

2) void fF (T &objT,int k) { k = objT.i+1; }

3) void T::fF (T &objT,int k) { k += objT.i; }

4) void fF (T &objT,int k) { objT.i += k; }

显而易见

纠错

Find out errors in the following code, and correct them.

1. Following is the destructor function prototype in Time class definition：

   void ~Time( int );

​ ~Time( );

1. Following is part of the Time class definition：

class Time { 

public: 
private:

int hour = 0; 
int minute = 0; 
int second = 0;

}; // end class Time

没眼看

模拟

Write the output of the following program.

#include<iostream> 
using namespace std; 
class test{ 
    private:

int num; 
float fl; 
public:
test(); 
int getint(){ return num;} 
float getfloat(){ return fl;}
~test();
};

test::test()
{

cout<<"Initailizing default"<<endl; 
    num = 0; fl = 0.0;

}

test::~test(){

cout<<"Destructor is active" <<endl;

}

int main()
{
    test array[2]; 
    cout<<array[1].getint()<< " " <<array[1].getfloat()<<endl;

}

Initailizing default
Initailizing default
0 0
Destructor is active
Destructor is active

此处float输出为0.

2.

#include <iostream> 
using namespace std; 
class A 
{ 
    public:

A() 
{ cout <<" A::A() called.\n";}
    virtual ~A() 
    { cout<<"A::~A() called.\n";}

};
class B: public A
{ 
    public:

B(int i)
{ 
    cout\<\<"B::B()called.\n"; 
         buf = new char\[i\];
}
    
virtual ~B()
{ delete [] buf;
 cout\<\< "B::~B() called.\n";
}

private:

char * buf;

}; 
void fun(A * a) { 
    delete a;

} 
void main() {

A * a = new B(15); 
    fun(a);

}

A::A() called.
B::B()called.
B::~B() called.
A::~A() called.

继承实际是在子类内部开了一个属于父类的空间。

无论继承还是声明为类的数据成员，都是先于该类被创建的，当然也会最后被析构。

3.

#include<iostream> 
using namespace std; 
class T 
{ 
public:

T(int x)
{ a=x; b*=x;}; 
    
static void display(T c)
{ cout<<"a="<<c.a<<'\t'<<"b="<<c.b<<endl; } 
    private:

int a; 
static int b;

} ;
int T::b=4; 
int main()
{

T A(3),B(2);

T::display(A);

T::display(B);

}

a=3 b=24
a=2 b=24

因为输出是后面的事，此时赋值全部完成了

4.

#include <iostream> 
using namespace std;
class B 
{ 
    int b; 
    public: B(int i) { b=i; } 
    virtual void virfun() 
    { cout<< "B::b: "<<b<<endl;
    }

};
class D: public B
{ int d; 
 public:

D(int i,int j): B(i) { d=j; }

void virfun() { B::virfun(); cout<<"D::d: "<<d<<endl; }

};

void fun(B *objp) { objp->virfun(); } 
void main() { B *pd ;
             pd=new B(3) ; 
             fun(pd);
             pd=new D(5,7); 
             fun(pd);

}

B::b: 3
B::b: 5
D::d: 7

5.

#include <iostream>

#include <string> 
#include <iomanip>
using namespace std; 
class Employee
{
    public:

Employee(const long k ,const char* str )
{
    number = k;
    strcpy_s(name,20,str); 
}
virtual ~Employee()
{ 
    name[0] = '\0';
}
const char * getName() const{ return name;} 
const long getNumber() const { return number;} 
virtual double earnings() const=0;
virtual void print() const 
{ cout <<number<<setw(16)<<name ;}

Employee * next;

protected:

long number; char name[20];

};


class Manager : public Employee 
{ 
    public:

Manager(const long k , const char str, double salary): Employee(k,str)

{ 
    setMonthlySalary(salary);
}

~Manager() { } 
    void setMonthlySalary(double salary) { monthlySalary = salary;} 
    virtual double earnings() const { return monthlySalary;} 
    virtual void print() const { Employee::print(); cout<<setw(16)\<\<"Manager\n";}

private:

double monthlySalary ;

};

class HourlyWorker : public Employee 
{ 
    public:

HourlyWorker(const long k , const char * str, double w=0.0, int h=0 ): Employee(k,str){ setWage(w); setHours(h);} 
    ~HourlyWorker(){} 
    void setWage(double w) { wage = w ;} 
    void setHours(int h) { hours = h ;} 
    virtual double earnings() const { return wage * hours ;} 
    virtual void print() const 
    {
        Employee::print(); cout<<setw(16)<<"Hours Worker\n"<< "\t\twageperhour "<<wage\<<" Hours"<<hours; 
    cout\<\<" earned \$"\<\<earnings()\<\<endl; 
    } 
    private:

double wage;
    double hours;
};


class PieceWorker : public Employee 
{ 
    public:

PieceWorker(const long k , const char * str, double wage =0.0, int quantity=0 ):Employee(k,str)
{ setWage(wage); setQuantity(quantity);}

~PieceWorker() { } 
    void setWage ( double wage ){ wagePerPiece = wage ;} 
    void setQuantity ( int q){ quantity = q ;} 
    virtual double earnings() const { return wagePerPiece * quantity; } 
    virtual void print() const 
    {
        Employee::print(); cout\<\<setw(16) \<\< "Piece Worker\n" ; 
        cout\<\<"\t\twagePerPiece "\<\< wagePerPiece\<\<" quantity "\<\<quantity; cout\<\<" eared \$" \<\< earnings() \<\<endl;
    }
    private:

double wagePerPiece; 
    int quantity;

}; 
void main()
{ 
    Employee * employ[3] ; 
    int i;
employ\[0\] = new Manager( 10135, "ZhangSan", 1200 ) ; 
    employ\[1\] = new HourlyWorker( 30712, "LiSi", 5, 260 ) ; 
    employ\[2\] = new PieceWorker( 20382, "Wangwu", 0.5, 2850 ) ; 
    cout << setiosflags(ios::fixed|ios::showpoint) << setprecision(2) ; 
    for( i = 0; i \<3; i ++ ) employ\[i\] -\> print() ; 
    for( i = 0; i \< 3; i ++ )
cout \<\<setw(8)\<\< employ\[i\]-\>getName() \<\< " " \<\<setw(10)\<\< employ\[i\] -\> earnings() \<\< endl ;

}

setiosflags(ios::fixed|ios::showpoint) 会使输出以固定小数点表示法显示，而不是使用科学计数法，并且总是显示小数点后的零。这个操作符作用于后续的浮点数输出。

setprecision(2) 设置输出浮点数的精度为2位小数。这意味着输出的浮点数将保留2位小数进行显示。
------------------------------------模式设置结束
10135 ZhangSan Manager
30712 LiSi Hours Worker
wageperhour 5.00 Hours 260.00 earned $1300.00
20382 Wangwu Piece Worker
wagePerPiece 0.50 quantity 2850 eared $1425.00
ZhangSan 1200.00
LiSi 1300.00
Wangwu 1425.00

可能需要学习手写setw和setprecision的样式

完善程序

fill in the blanks according to the output

1. The following program defined a complex class stands for complex number. It has real part real and imaginary part img. It overloaded complex number addition by using friend function. Please finish it.

   class complex
   {
       float [1], [2]; ---------------------------real img
       public:
   
   complex (float r=0,float i=0)
   
   { real=r; img=i; }
   
   [3] [4] operator+(complex c1,complex c2);---------------------friend complex
   
   };
   
   [5] operator+(complex c1,complex c2)-------------------------------complex
   
   { complex temp;
   
   [6]---------------------------------------------temp.real=cl.real+c2.real;
   [7]---------------------------------------------同理
   return temp;
   
   }

2. The following code has the screen output below, please fill in the blanks.

#include <iostream>
#include <math> 
using namespace std; 
class Power 
{ 
    public:
Power(int i)
{
    x=i;
}
*__*(8)___void display(){ cout<<"x="\<\<x;} -------virtual
    // definition of virtual function protected: int x;

};

class Square: public Power 
{
    public:

Square(int n):____(9)_________ { } //Constructor of Square void display()
    -----------------------------------------------Power(0)

{ _______ *（10）* ___cout\<\<”\tx square=”\<\<x\*x\<\<endl;}------Power::dispaly();

};

class Cube:public Power { public:

Cube(int n):Power(n){ } void display()

{ _______ *（10）* ___; cout\<\<”\tx cube=”\<\<x\*x\*x\<\<endl;}-------------Power::dispaly();

};

void fun(Power &p) { p.display();}

void main() 
{ 
    Square squ(2);

Cube cub(3); 
    fun(squ); fun(cub);

}

手抄

Write program

1．Use function template to calculate average of arrays of different data type. Function main () is as following:

#include <iostream>
using namespace std; 
void main()

{ 
    int a[]={ 1,2,3,4,5,6,7,8,9,10 }; 
    double b[]={ 1.1,2.2,3.3,4.4,5.5,6.6,7.7,8.8,9.9,10.0 }; 
    cout\<\< "Average of array a:" \<\<average(a,10)\<\<endl; 
    cout\<\< "Average of array b:" \<\<average(b,10)\<\<endl;
}

Program calculates average of an array of type integer and of type double. complete a function template to accomplish such function(功能) (6 points )

int average(int* arry,int _max)
{
    int temp=0;
    for(int i=;i<_max;i++)
    {
        temp+=arry[i];
    }
    temp/=_max;
    return temp;
}
double average(double* arry,int _max)
{
    int temp=0;
    for(int i=;i<_max;i++)
    {
        temp+=arry[i];
    }
    temp/=_max
    return temp;
}

Rewrite class Student, overload operator >> and \<\< to substitute(代替) function input() and output() respectively. （8 points）

1. Add a constructor for class Student to initiate data members ；（3 points）

2. Modify function main() to get correct result. （3 points）

#include <iostream> 
using namespace std;
class Student
{
char name[20]; 
    unsigned id; 
    double score; 
    public:
    void input()
{
cout\<\<"name? "; 
        cin\>\>name; 
        cout\<\<"id? "; 
        cin\>\>id;
cout\<\<"score? "; 
        cin\>\>score;
}
void output()
{
cout\<\<"name: "\<\<name\<\<"\tid: "\<\<id\<\<"\tscore: "\<\<score\<\<endl;
}
}; 
int main()
{
Student s; s.input();
s.output();
}

#include <iostream> 
using namespace std;
class Student
{
    friend ostream& operator>>(ostream& in,Student&)
    friend istream& operator<<(istream& in,Student&)
    private:
char name[20]; 
    unsigned id; 
    double score; 
    public:
    void input()
{
cout\<\<"name? "; 
        cin\>\>name; 
        cout\<\<"id? "; 
        cin\>\>id;
cout\<\<"score? "; 
        cin\>\>score;
};
    ostream& operator>>(ostream& in,Student&)
    {
        in>>name>>in>>score;
    }
void output()
{
cout\<\<"name: "\<\<name\<\<"\tid: "\<\<id\<\<"\tscore: "\<\<score\<\<endl;
}
}; 
int main()
{
Student s; s.input();
s.output();
}

总结：

1.重载运算符

1. 纯虚函数和抽象类
2. 课本上不知名的函数，如此处使用的复制，剪切等
3. 输出的样式
4. 生成的顺序