如何使用类创建矩形

Question

我需要创建一个程序，使用一个类从用户输入创建三个三角形，包括以下规范：

1. 私有数据应包含 4 个成员： 长度 宽度 区域 周长

2. 有 1 个具有以下参数的构造函数：长度和宽度。

3. 有 2 个突变体： setLength 设置/修改长度 和 setWidth 设置/修改宽度。

4. 有 5 个访问器： getLength 返回长度

   getWidth 返回宽度

   getPerimeter 返回周长

   getArea 返回区域

   printObjet 打印矩形的表示（使用相同的 前世的输出标准）

额外的功劳将您创建的 10 个矩形对象存储在一个向量中，并通过该向量排序以打印出 10 个矩形对象。一旦我知道如何完成主要任务，我相信我可以自己完成，尽管额外的帮助不会出错。

使用 DimChtz 的更改进行编辑后，代码如下。

#include <iostream>
using namespace std;

// Rectangle class declaration.
class Rectangle
{
   private:
      double width;
      double length;
      double area;
      double perimeter;


   public:
      void setWidth(double);
      void setLength(double);
      double getWidth();
      double getLength();
      double getArea();
      double getPerimeter();
      void printObjet();
      void calc();
      Rectangle();
};

//beginning class constructor
Rectangle::Rectangle() {
    this->width = 0;
    this->length = 0;
    this->area = 0;
    this->perimeter = 0;
}
// main class constructor
Rectangle::Rectangle(double width, double length)
{   this->width = width;
    this->length = length;
    this->calc();
}
//calc calculates the area and perimeter from width and length.
void Rectangle::calc() {
    this->area = this->width * this->length;
    this->perimeter = 2 * (this->width + this->length); }

// the class functions definition
// setWidth assigns its argument to the private member width.
void Rectangle::setWidth(double width)
{   this->width = width;
    this->calc(); }

// setLength assigns its argument to the private member length.
void Rectangle::setLength(double length)
{   this->length = length;
    this->calc(); }

// getLength returns the value in the private member length.
double Rectangle::getLength()
{   return length; }

// getWidth returns the value in the private member width.
double Rectangle::getWidth()
{   return width; }

// getPerimeter returns parameter of box.
double Rectangle::getPerimeter()
{   return  this->perimeter; }

// getArea returns area of box.
double Rectangle::getArea()
{   return this->area; }

// printObjet prints the data of the rectangle
void Rectangle::printObjet()
{   cout << "  Width = " << getWidth() << endl;
    cout << "  Length = " << getLength() << endl;
    cout << "  Perimeter = " << getPerimeter() << endl;
    cout << "  Area = " << getArea() << endl << endl; }


// the main program
int main()
{
   double width;     // Local variable for width.
   double length;   // Local variable for length.

    // create object using constructor
   Rectangle   box1;
   Rectangle   box2;
   Rectangle   box3;

   // Get the 1st rectangle's width and length from the user.
   cout << "Enter the length of the 1st rectangle: ";
   cin >> length;
   cout << length << endl;
   cout << "Enter the width of the 1st rectangle:  ";
   cin >> width;
   cout << width << endl;


    // Store the width and length of the rectangle in the box1 object.
    box1.setWidth(width);
    box1.setLength(length);

         // Display box1 data.
    cout << "You created a rectangle with the following characteristics:" << endl << endl;
    box1.printObjet();


    // Get the 2nd rectangle's width and length from the user.
    cout << "Enter the length of the 2nd rectangle: ";
    cin >> length;
    cout << length << endl;
    cout << "Enter the width of the 2nd rectangle:  ";
    cin >> width;
    cout << width << endl;

        // Store the width and length of the rectangle in the box1 object.
        box2.setWidth(width);
        box2.setLength(length);

         // Display box2 data.
         cout << "You created a rectangle with the following characteristics:" << endl << endl;
         box2.printObjet();

    // Get the 3rd rectangle's width and length from the user.
    cout << "Enter the length of the 3rd rectangle: ";
    cin >> length;
    cout << length << endl;
    cout << "Enter the width of the 3rd rectangle:  ";
    cin >> width;
    cout << width << endl;

        // Store the width and length of the rectangle in the box1 object.
        box3.setWidth(width);
        box3.setLength(length);

            // Display box3 data.
            cout << "You created a rectangle with the following characteristics:" << endl << endl;
            box3.printObjet();

   return 0;
}

现在是编译错误

34:1: error: prototype for 'Rectangle::Rectangle(double, double)' does not match any in class 'Rectangle'
 Rectangle::Rectangle(double width, double length)

5:7: error: candidates are: constexpr Rectangle::Rectangle(Rectangle&&)
 class Rectangle

5:7: error:                 constexpr Rectangle::Rectangle(const Rectangle&)

27:1: error:                 Rectangle::Rectangle()

Answer 1

1) 实际上，您不使用area 和perimeter。每次修改 width 和/或 length 时，都应该计算 area 和 perimeter：

Rectangle::Rectangle(double width, double length) {
    this->width = width;
    this->length = length;
    this->calc();
}

void Rectangle::setWidth(double width) {
    this->width = width;
    this->calc();
}

void Rectangle::setLength(double length) {
    this->length = length;
    this->calc();
}

double Rectangle::getPerimeter() { return  this->perimeter; }

double Rectangle::getArea() { return this->area; }

现在你需要一个新的私有函数：

void Rectangle::calc() {
    this->area = this->width * this->length;
    this->perimeter = 2 * (this->width + this->length);
}

2) 你需要稍微改变一下printObjet：

void printObjet();
// ...
void Rectangle::printObjet() {
    cout << "  Width = " << getWidth() << endl << "  Length = " << getLength() << endl << "  Perimeter = " << getPerimeter() << endl<< "  Area = " << getArea() << endl << endl;
}

然后改变：

cout << box1.printObjet();

到：

box1.printObjet();

3) 你需要这个：

Rectangle();

// ...

Rectangle::Rectangle() {
    this->width = 0;
    this->length = 0;
    this->area = 0;
    this->perimeter = 0;
}

或者简单地说：

Rectangle::Rectangle() : width(0), length(0), area(0), perimeter(0) {  }

甚至：

Rectangle::Rectangle() : Rectangle(0.0, 0.0) {  }