纯基类 c++ 的动态数组出现问题
Trouble with dynamic array of pure base class c++
我有一个介绍 c++ 类的编程作业。该程序应该使用虚函数来输入，计算和显示与各种形状相关的数量。Shape 类必须包含所有纯虚函数：显示、获取维度、面积、周长和体积。
程序驱动程序必须将 20 个指针的数组分配给 Shape，然后使用输入的对象重复填充数组。
我的程序在进入显示调用时退出。因此，我认为这意味着我的getDimensions或显示函数无法正常工作。我花了几个小时试图解决这个问题，如果有人能指出我正确的方向，似乎找不到到底出了什么问题。
这是我的代码：
#include <iostream>
#include <cmath>
using namespace std;
const double PI=3.141592654;
class Shape
{
protected:
double x, y;
public:
Shape(): x(1.0),y(1.0){}
Shape(double a, double b): x(a),y(b){}
virtual void display()=0;
virtual void getDimensions()=0;
virtual double area()=0;
virtual double perimeter()=0;
virtual double volume()=0;
};
class Rectangle: public Shape
{
public:
Rectangle():Shape(){}
Rectangle(double a, double b):Shape(a,b){}
void display();
void getDimensions()
{
cout<<"Input for Rectangle - "
<<"enter length and width: ";
cin>>x>>y;
}
double area()
{return x*y;}
double perimeter()
{return (2*x)+(2*y);}
double volume()
{return 0;}
};
class Circle: public Shape
{
private:
double radius;
public:
Circle(): radius(1.0){}
Circle(double r): radius(r){}
void display();
void getDimensions()
{
cout<<"Input for Circle - enter radius: ";
cin>>radius;
}
double area()
{return PI*radius*radius;}
double perimeter()
{return 2*PI*radius;}
double volume()
{return 0;}
};
class Triangle: public Shape
{
private:
double z;
public:
Triangle():z(1.0), Shape(){}
Triangle(double f, double g, double w):z(w), Shape(f,g){}
void display();
void getDimensions()
{
cout<<"Input for Triangle - "
<<"enter side 1, side 2, side 3: ";
cin>>x>>y>>z;
}
double area()
{
double half, underroot;
half = perimeter()/2;
underroot = half*(half-x)*(half-y)*(half-z);
return sqrt(underroot);
}
double perimeter()
{return x+y+z;}
double volume()
{return 0;}
};
class Box: public Shape
{
private:
double p;
public:
Box():p(1.0), Shape(){}
Box(double a, double b, double c): Shape(a,b), p(c){}
void display();
void getDimensions()
{
cout<<"Input for Box - "
<<"enter length, width, and height: ";
cin>>x>>y>>p;
}
double area()
{return (2*x*y)+(2*x*p)+(2*y*p);}
double perimeter()
{return 0;}
double volume()
{return x*y*p;}
};
class Can: public Shape
{
public:
Can():Shape(){}
Can(double r, double h):Shape(r,h){}
void display();
void getDimensions()
{
cout<<"Input for Can - "
<<"enter radius and height: ";
cin>>x>>y;
}
double area()
{
double base;
base = PI*x*x;
return (2*PI*x*y)+(2*PI*x*x);
}
double perimeter()
{return 0;}
double volume()
{return PI*x*x*y;}
};
class Cone: public Shape
{
public:
Cone():Shape(){}
Cone(double r, double h):Shape(r, h){}
void display();
void getDimensions()
{
cout<<"Input for Cone - "
<<"enter radius and height: ";
cin>>x>>y;
}
double area()
{
double underroot;
underroot = sqrt((x*x)+(y*y));
return (PI*x*x)+(PI*x*underroot);
}
double perimeter()
{return 0;}
double volume()
{return (1/3)*PI*x*x*y;}
};
class Ball: public Shape
{
private:
double radius;
public:
Ball():radius(1.0){}
Ball(double r):radius(r){}
void display();
void getDimensions()
{
cout<<"Input for Ball - "
<<"enter radius: ";
cin>>radius;
}
double area()
{return 4*PI*radius*radius;}
double perimeter()
{return 0;}
double volume()
{return (4/3)*PI*radius*radius*radius;}
};
int main()
{
int cnt=0, cnt2=0, choice;
char yorn;
Shape *sPtr[20];
while(cnt<20)
{
cnt++;
cnt2++;
cout<<"nIt is time to enter your shape selection"
<<" and dimensions.n"
<<"Enter the number of the shape type: n"
<<"t1 - Rectanglen"
<<"t2 - Circlen"
<<"t3 - Trianglen"
<<"t4 - Boxn"
<<"t5 - Cann"
<<"t6 - Conen"
<<"t7 - Balln"
<<"=> ";
cin>>choice;
while (choice<1||choice>7)
{
cout<<"Invalid selection. Re-enter: n"
<<"=> ";
cin>>choice;
}
switch (choice)
{
case 1:
{
sPtr[cnt]=new Rectangle;
sPtr[cnt]->getDimensions();
break;
}
case 2:
{
sPtr[cnt]=new Circle;
sPtr[cnt]->getDimensions();
break;
}
case 3:
{
sPtr[cnt] = new Triangle;
sPtr[cnt]->getDimensions();
break;
}
case 4:
{
sPtr[cnt] = new Box;
sPtr[cnt]->getDimensions();
break;
}
case 5:
{
sPtr[cnt] = new Can;
sPtr[cnt]->getDimensions();
break;
}
case 6:
{
sPtr[cnt] = new Cone;
sPtr[cnt]->getDimensions();
break;
}
case 7:
{
sPtr[cnt] = new Ball;
sPtr[cnt]->getDimensions();
break;
}
}
cout<<"nSelect another shape? (y or n): ";
cin>>yorn;
if(yorn=='n'||yorn=='N')
cnt=20;
}
for(int i=0; i<cnt2; i++)
{
sPtr[i]->display();
}
return 0;
}
void Rectangle::display()
{
cout<<"nRectangle: "
<<"nDimensions: "
<<"Length: "<<x<<"nWidth: "<<y
<<"nArea: "<<area()
<<"nPerimeter: "<<perimeter();
}
void Circle::display()
{
cout<<"nCircle: "
<<"nDimensions: "
<<"nRadius: "<<radius
<<"nArea: "<<area()
<<"nPerimeter: "<<perimeter();
}
void Triangle::display()
{
cout<<"nTriangle: "
<<"nDimensions: "
<<"nSide 1: "<<x
<<"nSide 2: "<<y
<<"nSide 3: "<<z
<<"nArea: "<<area()
<<"nPerimeter: "<<perimeter();
}
void Box::display()
{
cout<<"nBox: "
<<"nDimensions: "
<<"nLength: "<<x
<<"nWidth: "<<y
<<"nHeight: "<<p
<<"nSurface area: "<<area()
<<"nVolume: "<<volume();
}
void Can::display()
{
cout<<"nBox: "
<<"nDimensions: "
<<"nRadius: "<<x
<<"nHeight: "<<y
<<"nSurface area: "<<area()
<<"nVolume: "<<volume();
}
void Cone::display()
{
cout<<"nCone: "
<<"nDimensions: "
<<"nRadius: "<<x
<<"nHeight: "<<y
<<"nSurface area: "<<area()
<<"nVolume: "<<volume();
}
void Ball::display()
{
cout<<"nBall: "
<<"nDimensions: "
<<"nRadius: "<<radius
<<"nSurface area: "<<area()
<<"nVolume: "<<volume();
}
您从 0 开始显示：
for(int i=0; i<cnt2; i++)
{
sPtr[i]->display();
}
但是您从 1 开始添加到sPtr：
int cnt=0;
while(cnt<20)
{
cnt++;
...
sPtr[cnt] = new ...;
}
这些类型的错误是首选使用std::vector<Shape*>而不是原始数组和计数器的重要原因。然后你可以只写以下内容，这不太容易出错：
std::vector<Shape*> shapes;
while (shapes.size() < 20) {
...
shapes.push_back(new Rectangle);
...
}
for (size_t i = 0; i < shapes.size(); ++i) {
shapes[i]->display();
}
或者真的，在 C++11 中，这应该是一个vector<unique_ptr<Shape>>.
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