C++编程练习：抽象类——编写一个程序，计算三角形、正方形的面积，抽象出一个基类base。

#pragma once        //只运行一次头文件
#include <iostream>
using namespace std;
class base
{
public:
  virtual void display() = 0;   //成员函数dispaly（）声明为纯虚函数
};
class Square : virtual public base     //派生类Square正方形
{
protected:
  float x;
public:
  float width;
  Square()
  {
  }
  Square(float a)
  {
  x = a;
  }
  virtual float getSquare()
  {
  return (x * x);
  }
  virtual void display()
  {
  cout << "正方形的边长为：" << x << endl;
  cout << "正方形的面积为：" << getSquare() << endl;
  }
};
class Rectangle : virtual public base    //派生类Rectangle三角形
{
protected:
  int a, h;
public:
  Rectangle()
  {
  }
  Rectangle(int a1, int h1)
  {
  a = a1;
  h = h1;
  }
  virtual float getRectangle()
  {
  return (a * h) / 2.0;
  }
  virtual void display()
  {
  cout << "三角形的底和高为：" << a << endl << h << endl;
  cout << "三角形的面积为：" << getRectangle() << endl;
  }
};

#include <iostream>
#include "headfile.h"
using namespace std;
int main()
{
  base* p;
  double a = 0, a1 = 0, h1 = 0;
  cout << "请输入正方形的边长：" << endl;
  cin >> a;
  Square A(a);
  p = &A;
  p->display();
  cout << "" << endl;
  cout << "请输入三角形的底和高：" << endl;
  cin >> a1 >> h1;
  Rectangle B(a1, h1);
  p = &B;
  p->display();
  system("pause");
  return 0;
}