update

practical_exercises/10_day_practice/day6/纯虚函数和抽象类/抽象类.cpp

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+#include<iostream>
+using namespace std;
+class Figure{
+    protected:
+        double x,y;
+    public:
+        void set(double i, double j){
+            x=i;y=j;
+        }
+        virtual void area()=0;
+};
+
+class Trianle:public Figure{
+    public:
+        void area(){
+            cout<<"三角形面积："<<x*y*0.5<<endl;
+        }
+};
+class Rectangle:public Figure{
+    public:
+        void area(){
+            cout<<"这是矩形，它的面积是："<<x*y<<endl;
+        }
+};
+
+int main(int argc, char const *argv[])
+{
+    //定义抽象类指针
+    Figure *pF=NULL;
+    // Figure f1; 抽象类不能被实例化
+    Rectangle r;
+    Trianle t;
+    t.set(10,20);
+    pF=&t;
+    pF->area();
+    r.set(10,20);
+    pF=&r;
+    pF->area();
+    //定义抽象类引用
+    Figure &rF=t;
+    rF.set(20,20);
+    rF.area();
+    system("pause");
+    return 0;
+}
+