預期在“ *”之前的主要表達式？

Question

我已經仔細閱讀了所有這些內容，並且對使用c ++進行編碼還比較陌生，只是不知道自己缺少什么。 有任何想法嗎？

我的錯誤發生在第45行“ return pi *（Radius * Radius）;”。 我幾乎肯定該行的語法正確，但是為什么我會遇到編譯錯誤。

#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;
}

謝謝大衛

Answer 1

現在，我看到您在基類中有一個成員，該成員的名稱Radius與派生類中的名稱相同，這是導致錯誤的原因。 解決方案是使用基類名稱對其進行限定：

更改：

return pi * (Radius * Radius);

至：

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

這個附加的： double radius; 可能來自一些測試-對嗎？

[編輯]

從設計的角度來看， class Radius : public Circle的存在class Radius : public Circle沒什么意義，僅使用Circle來獲取其半徑應該沒問題。

Answer 2

#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;}
    float getArea(){return length*width;}
};

class Circle
{
    protected:
    float Radius;
public:
    Circle(): Radius(0)     {cout<<"Enter Radius: "; cin>>Radius;}
    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";
        Rectangle a;
        cout<<"Area = "<<a.getArea()<<" square\n\n";
        break;}

    //Circle option:
    case 'C':
    case 'c': {
        cout<<"Enter data for circle to find radius.\n";
        Circle 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;
}