std::cout << circle.getArea() << std::endl;

std::cout << circle.getArea() << std::endl; 是一行C++代码，用于输出圆的面积到标准输出流。这行代码中，std::cout 是一个输出流对象，<< 是输出运算符，circle.getArea() 是调用圆对象的 getArea() 方法来获取圆的面积，std::endl 是用于输出换行符的特殊符号。

相关问题:
1. 什么是标准输出流(std::cout)？
2. circle.getArea() 是什么意思？
3. 为什么要使用 std::endl 而不是普通的换行符？

相关问题

Shape类派生了Circle类和Rectangle类，请阅读主函数代码，完成Shape类、Circle类、Rectangle类的定义 【样例输入】 无 【样例输出】 Rectangle: Width=3.5,Height=7.2 Area=25.2 Perimeter=21.4 Circle: R=2.3 Area=16.619 Perimeter=14.4513 Shape Area=0 Perimeter=0 #include <iostream> #define PI 3.14159 using namespace std; class Shape { }; class Circle:public Shape { }; class Rectangle:public Shape { }; int main() { Rectangle recObj(7.2,3.5); recObj.print(); cout<<"Area="<<recObj.getArea()<<" Perimeter="<<recObj.getPerimeter()<<endl; Circle circleObj(2.3); circleObj.print(); cout<<"Area="<<circleObj.getArea()<<" Perimeter="<<circleObj.getPerimeter()<<endl; Shape shapeObj; shapeObj.print(); cout<<"Area="<<shapeObj.getArea()<<" Perimeter="<<shapeObj.getPerimeter()<<endl; return 0; }

完成代码如下：

#include <iostream>
#define PI 3.14159
using namespace std;

class Shape {
public:
    virtual void print() {
        cout << "Shape";
    }
    virtual double getArea() {
        return 0;
    }
    virtual double getPerimeter() {
        return 0;
    }
};

class Circle : public Shape {
private:
    double r;
public:
    Circle(double r) {
        this->r = r;
    }
    void print() {
        cout << "Circle: R=" << r;
    }
    double getArea() {
        return PI * r * r;
    }
    double getPerimeter() {
        return 2 * PI * r;
    }
};

class Rectangle : public Shape {
private:
    double width, height;
public:
    Rectangle(double width, double height) {
        this->width = width;
        this->height = height;
    }
    void print() {
        cout << "Rectangle: Width=" << width << ",Height=" << height;
    }
    double getArea() {
        return width * height;
    }
    double getPerimeter() {
        return 2 * (width + height);
    }
};

int main() {
    Rectangle recObj(7.2, 3.5);
    recObj.print();
    cout << "  Area=" << recObj.getArea() << "  Perimeter=" << recObj.getPerimeter() << endl;

    Circle circleObj(2.3);
    circleObj.print();
    cout << "  Area=" << circleObj.getArea() << "  Perimeter=" << circleObj.getPerimeter() << endl;

    Shape shapeObj;
    shapeObj.print();
    cout << "  Area=" << shapeObj.getArea() << "  Perimeter=" << shapeObj.getPerimeter() << endl;

    return 0;
}

输出结果为：

Rectangle: Width=7.2,Height=3.5  Area=25.2  Perimeter=21.4
Circle: R=2.3  Area=16.619  Perimeter=14.4513
Shape  Area=0  Perimeter=0

请编程实现：定义一个基类Shape，在此基础上派生出Rectangle和Circle，三者都有getArea()函数计算对象的面积。使用Rectangle类创建一个派生类Square。注意基本数据类型使用float类型。 其中主函数如下： int main() { Shape s1; cout << "The area of the Shape is " << s1.getArea () << endl; Rectangle s2(4,6); cout << "The area of the Rectangle is " << s2.getArea() << endl; Square s3(5); cout << "The area of the Square is " << s3.getArea() << endl; return 0; }

以下是题目的代码实现：

#include<iostream>
using namespace std;

class Shape{
public:
    virtual float getArea(){
        return 0;
    }
};

class Rectangle: public Shape{
private:
    float length;
    float width;
public:
    Rectangle(float l, float w){
        length = l;
        width = w;
    }
    virtual float getArea(){
        return length * width;
    }
};

class Circle: public Shape{
private:
    float radius;
public:
    Circle(float r){
        radius = r;
    }
    virtual float getArea(){
        return 3.1415 * radius * radius;
    }
};

class Square: public Rectangle{
public:
    Square(float a): Rectangle(a,a){}
};

int main(){
    Shape s1;
    cout << "The area of the Shape is " << s1.getArea() << endl;

    Rectangle s2(4,6);
    cout << "The area of the Rectangle is " << s2.getArea() << endl;

    Square s3(5);
    cout << "The area of the Square is " << s3.getArea() << endl;

    return 0;
}

程序的输出结果：

The area of the Shape is 0
The area of the Rectangle is 24
The area of the Square is 25

其中，基类Shape中的getArea()函数返回0，因为无法计算Shape的面积。派生类Rectangle和Circle分别计算矩形和圆的面积，Square继承自Rectangle，并重写了构造函数，使得正方形的长和宽相等，从而实现了正方形的面积计算。