4.27

 1 #include<iostream>
 2 using namespace std;
 3 class Rectangle {
 4 public:
 5     int j;
 6     void area(int X = 0, int Y = 0, int A = 0, int B = 0);
 7 private:
 8     int x, y, a, b;
 9 };
10 void Rectangle::area(int X, int Y, int A, int B) {
11     x = X; y = Y; a = A; b = B;
12     j = (a - x) * (b - y);
13 }
14 int main() {
15     int x, y, a, b;
16     Rectangle rectangle;
17     cout << "输入左下角坐标x和y" << endl;
18     cin >> x >> y;
19     cout << "输入右上角坐标为a和b" << endl;
20     cin >> a >> b;
21     rectangle.area(x, y, a, b);
22     cout << "该矩形面积为：" << rectangle.j << endl;
23     return 0;
24 }

 1 #include <iostream>
 2 using namespace std;
 3 class rectangle { 
 4 public:
 5     rectangle(double len, double wide) {
 6         length = len;
 7         widen = wide;
 8     }
 9     ~rectangle() {};
10     double getarea() { return length * widen; }
11     double getlength() { return length; }
12     double getwiden() { return widen; }
13 private:
14     double length;
15     double widen;
16 };
17 void main() { 
18     double length, widen;
19     cout << "请输入矩形的长：";
20     cin >> length;
21     cout << "请输入矩形的宽：";
22     cin >> widen;
23     rectangle r(length, widen); 
24     cout << "长为" << length << "，宽为" << widen << "的矩形面积是" << r.getarea() << endl;
25 }
26  

 1 #include <iostream>
 2 using namespace std;
 3 class circle {  
 4 public:
 5     circle(double radius) {
 6         r = radius;
 7     }
 8     ~circle() {};  
 9     double getarea() { return 3.14 * r * r; }
10 private:
11     double r;
12 };
13 void main() { 
14     cout << "请输入圆的半径：";
15     double radius;
16     cin >> radius;
17     circle r(radius);
18     cout << "圆的面积是：" << r.getarea() << endl;  
19 }