'float*' 和 'float*' 類型的無效操作數到二進制 'operator*'

Question

我不知道為什么我會收到這個錯誤。 就像a*a將a*視為指針（ float*到float*是否與float到float相同）。 顯然，當我在子類中聲明a時，問題得到了解決，但關鍵是我希望我的子類自動從我的父類 class 獲得它。

當我添加“float a;”時還有一件事到程序可以運行的每個子類。 所以我這樣做只是為了測試它是否有效，但沒有。 浮點數 a 在 setA 中沒有值。 我剛剛添加了 cout<<a; 在a = b之后;。

#include"Oblik.h"
#include<cmath>

using namespace std;

class Jednakostranicni : public GeometrijskaFigura{

    float P(){
        return (a*a*sqrt(3))/4; //12    13  C:\Users\Name\Desktop\prvi.cpp  [Error] invalid operands of types 'float*' and 'float*' to binary 'operator*'
    }
    float O(){
        return a+a+a; //15  12  C:\Users\Name\Desktop\prvi.cpp  [Error] invalid operands of types 'float*' and 'float*' to binary 'operator+'
    }
    
};

class Kvadrat : public GeometrijskaFigura{
    
    float P(){
        return a*a;//23 12  C:\Users\Name\Desktop\prvi.cpp  [Error] invalid operands of types 'float*' and 'float*' to binary 'operator*'
    }
    float O(){
        return a+a+a+a;//26 12  C:\Users\Name\Desktop\prvi.cpp  [Error] invalid operands of types 'float*' and 'float*' to binary 'operator+'
    }
    
};

class Krug : public GeometrijskaFigura{
    
    float P(){
        return a*a*3.14;//34    12  C:\Users\Name\Desktop\prvi.cpp  [Error] invalid operands of types 'float*' and 'float*' to binary 'operator*'
    }
    float O(){
        return 2*a*3.14;//37    12  C:\Users\Name\Desktop\prvi.cpp  [Error] invalid operands of types 'int' and 'float*' to binary 'operator*'
    }
    
};

int main(){
    
    GeometrijskaFigura *f;
    int x;
    
    cin>>x;
    
    f->setA(x);
    
    f=new Jednakostranicni;
    cout<<"Jednakostranicni-P: "<<f->P()<<" O: "<<f->O()<<endl;
    f=new Kvadrat;
    cout<<"Kvadrat-P: "<<f->P()<<" O: "<<f->O()<<endl;
    f=new Krug;
    cout<<"Krug-P: "<<f->P()<<" O: "<<f->O()<<endl;
    
    
    
    return 1;
    
    
}

// this is Oblik.h file code
#include<iostream>

using namespace std;

class GeometrijskaFigura{
    protected: float a;
    public:
        
        void setA(float b){
         a=b;
        }
        
        virtual float P()=0;
        virtual float O()=0;
};

Answer 1

您有未定義的行為，因為f未初始化：

GeometrijskaFigura *f;
int x;
    
std::cin >> x;
    
f->setA(x); // UB: use uninitialized f.

應該

int a;

std::cin >> a;

Jednakostranicni j;
j.setA(a);
std::cout << "Jednakostranicni-P: " << a.P() << " O: " << a.O() << std::endl;

Kvadrat k;
k.setA(a);
std::cout << "Kvadrat-P: " << k.P() << " O: " << k.O() << std::endl;

Krug krug;
krug.setA(a);
std::cout << "Krug-P: " << krug.P() << " O: " << krug.O() << std::endl;