c++ - '*'之前的预期主表达式？

我已经仔细研究了所有这些内容，并且对编写c++还是比较陌生，只是不知道自己缺少什么。有任何想法吗？

我的错误发生在第45行“return pi *(Radius * Radius);”。我几乎肯定该行的语法正确，但是为什么我会遇到编译错误。

#include <iostream>
#include <cstdlib>

using namespace std;
const double pi = 3.14159;

class Rectangle
{
protected:
   float length, width;
public:
    Rectangle(): length(0), width(0)
    {
        cout<<"Enter length: "; cin>>length;
        cout<<"Enter width: "; cin>>width;
    }
};

class Circle
{
    protected:
    float Radius;
public:
    double radius;
    Circle(): Radius(0)
    {
        cout<<"Enter Radius: "; cin>>Radius;
    }
};

class Area : public Rectangle
{
public:
   float getArea()
     {
         return length*width;
     }
};

class Radius : public Circle
{
    public:
   float getRadius()
     {
         return pi * (Radius * Radius);
     }
};

int main()
{
char choice;
for (int i = 0; i < 4; i++)  //loop statement
{
cout << "Program to Find Area of a Square and Circle" << endl <<                         //selection of which calculation to run
        "Enter S for square square." << endl <<
        "Enter C for circle." << endl <<
        "Enter Q to Quit the program." << endl << endl <<
        "Enter an option above: ";
cin >> choice;

switch(choice)
    {
    //Square option:
    case 'S':
    case 's': {
        cout<<"Enter data for rectangle to find area.\n";
        Area a;
        cout<<"Area = "<<a.getArea()<<" square\n\n";
        break;}

    //Circle option:
    case 'C':
    case 'c': {
        cout<<"Enter data for circle to find radius.\n";
        Radius c;
        cout<<"Radius = "<<c.getRadius()<<" meter\n\n";
        break;}

    //Quit option:
    case 'Q':
    case 'q': {
        cout << "Thank you for using Area Application" << endl << endl;
        system("PAUSE");
        return EXIT_SUCCESS;
    break;}

    //default option binds to a non-selected choice function:
    default:
        cout << choice << " is not a valid selection." << endl;
        cout << "Select a valid shape choice: S or C" << endl << endl;
    break;
    }
}

cout << "Press enter to continue ..." << endl;
return EXIT_SUCCESS;
}

谢谢
大卫

最佳答案

现在，我看到您在基类中有一个成员，该成员的名称Radius与派生类中的名称相同，这就是导致错误的原因。解决方案是使用基类名称对其进行限定:

更改:

return pi * (Radius * Radius);

至:

return pi * (Circle::Radius * Circle::Radius);

这个附加的:double radius;可能来自一些测试-对吗？

[编辑]

从设计的 Angular 来看，class Radius : public Circle的存在意义不大，仅使用Circle来获得半径就可以了。

关于c++ - '*'之前的预期主表达式？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/37591683/