Third class exercise

One 、 Single topic selection

2-1
The following incorrect statements about classes and objects are （ C）.

A. Object is an instance of a class
B. Any object can only belong to a specific class
C. A class can only have one object
D. The relationship between classes and objects is similar to that between data types and variables

2-2
Class instantiation refers to （ B）.

A. Defining classes
B. Define the object
C. Call the member function of the class
D. Access the data members of the object

2-3
In the description of the characteristics of member functions ,（B ） It's wrong. .

A. Member functions can be overloaded
B. Member functions must be inline functions
C. A class can have no member functions
D. Member functions can set the default value of parameters

2-4
If... Is not used in the class definition private、protected、 or public keyword , Then all members （ C）

A. All are public member
B. All are proctected member
C. All are private member
D. not always

2-5
In an object-oriented system , Objects are basic runtime entities , it C___ .

A. Only data can be included ( attribute )
B. Only operations can be included ( Behavior )
C. Encapsulate attributes and behaviors as a whole
D. Must have an explicitly defined object name

2-6
In an object-oriented system , The property of an object is __C______.

A. Behavior characteristics of objects
B. How to associate with other objects
C. Distinguishing features from other objects
D. How to interact with other objects

Two 、 Completion

1.（4 branch ）The public members provide the class’s interface and the private members provide implementation details. Members are accessed using . (dot) for objects and −> (arrow) for pointers.

2.（2 branch ）A struct is a class where members are by default public

3、 ... and 、 Function questions

6-1 Class declaration and implementation of member functions

fraction 10
author Li Tingyuan
Company China Academy of Civil Aviation
Declared a Dog class , Contains age,weight Equal attribute , And how to operate on these properties . Please implement the member function of this class .

Dog Class is declared as follows ：
class Dog {
public:
void setAge(int a);
int getAge();
void setWeight(int w);
int getWeight();
private:
int age, weight;
};
Please implement Dog class .

Sample referee test procedure ：
#include
using namespace std;

class Dog {
public:
void setAge(int a);
int getAge();
void setWeight(int w);
int getWeight();
private:
int age, weight;
};

int main()
{
Dog d;
int a, w;
cin >> a >> w;
d.setAge(a);
d.setWeight(w);
cout << d.getAge() << endl;
cout << d.getWeight() << endl;
return 0;
}

/* Your code will be embedded here */
sample input ：
1 3
sample output ：
1
3

void Dog :: setAge(int a) {
    
    age = a;
}
void Dog :: setWeight(int w) {
    
    weight = w;
}
int Dog :: getAge() {
    
    return age;
}
int Dog :: getWeight() {
    
    return weight;
}

6-2 Use the class to calculate the area of the rectangle

fraction 10
author Li Tingyuan
Company China Academy of Civil Aviation
Define and implement a rectangle class , It has two properties: length and width , Calculate the area of the rectangle by the member function .

Rectangle class Rectang The interface is defined as follows ：
class Rectangle {
public:
void setLength(int l);// Set the length of the rectangle
void setWidth(int w); // Set the width of the rectangle
int getArea(); // Calculates and returns the area of the rectangle
private:
int length, width; // The length and width of the rectangle
};
Please implement Rectangle class .

Sample referee test procedure ：
#include
using namespace std;

class Rectangle {
public:
void setLength(int l);// Set the length of the rectangle
void setWidth(int w); // Set the width of the rectangle
int getArea(); // Calculates and returns the area of the rectangle
private:
int length, width; // The length and width of the rectangle
};

int main()
{
Rectangle r;
int len, w;
cin >> len >> w;
r.setLength(len);
r.setWidth(w);
cout << r.getArea() << “\n”;

return 0;

}

/* Your code will be embedded here */
sample input ：
10 20
sample output ：
200

void Rectangle :: setLength(int l) {
    
    length = l;
}
void Rectangle :: setWidth(int w) {
    
    width = w;
}
int Rectangle :: getArea() {
    
    return length * width;
}

6-3 Define a name Stock Our stock class

fraction 10
author Zhang Dehui
Company Xi'an University of Posts and Telecommunications
Define a name Stock Our stock class , This class includes ： A group called symbol The string represents the stock code . A group called name The string data member of represents the stock name . A group called previousClosingPrice Of double Data member , It stores the closing price of the previous day . A group called currentPrice Data member , It stores the current stock transaction price . Create a to set the stock code and stock name set( ) function . A group called changePercent() Function returns the range of stock price rise and fall .（ From previousClosingPrice Change to currentPrice Percent of .）
### Class called ：

Stock
Sample referee test procedure ：
#include
using namespace std;
/* The code you submit will be embedded here */

int main( ) {
char s1[10],n1[20];
cin>>s1>>n1;
Stock stock;
stock.set(s1, n1);
// Enter the closing price of the previous day
cin>>stock.previousClosingPrice;

//  Enter the current transaction price 
cin>>stock.currentPrice;

//  Show stock information 
cout<<stock.name<<" price changed: " <<(stock.changePercent() * 100)<<"%";
return 0;

}

sample input ：
002594
BYD
56.98
55.40
sample output ：
BYD price changed: -2.7729%

class Stock{
    
    public:
        char* symbol;
        char* name;
        double previousClosingPrice;
        double currentPrice;
    public:
        void set(char* s,char* n){
    
            symbol = s;
            name = n;
        }
    
        double changePercent(){
    
            return (currentPrice-previousClosingPrice)/previousClosingPrice;
        }
};