函数重载问题，为什么a会重定义

# include <iostream>
using namespace std;
# include <iomanip>
# include <math.h>
class Rectangle
{
    double area;
public:
    Rectangle()
    {
        double area = 0;
    }
    Rectangle(double a);
    Rectangle(double b, double c);

};


int main()
{
    double a, b, c;
    cout << "计算正方形面积（输入边长）" << endl;
    cin >> a;
    Rectangle(a);
    cout << "计算长方形面积（输入长和宽）" << endl;
    cin >> b >> c;
    Rectangle(b, c);
    return 0;
}
Rectangle::Rectangle(double x)
{
    double area = x * x;
    cout << "正方形面积为：" << endl;
    cout << area << endl;
}
Rectangle::Rectangle(double b, double c)
{
    double area = c * b;
    cout << "长方形面积为：" << endl;
    cout << area << endl;
}

修改如下：

# include <iostream>
using namespace std;
# include <iomanip>
# include <math.h>
class Rectangle
{
    double area;
public:
    Rectangle()
    {
        double area = 0;
    }
    Rectangle(double a);
    Rectangle(double b, double c);
};
 
int main()
{
    double a, b, c;
    cout << "计算正方形面积（输入边长）" << endl;
    cin >> a;
    Rectangle T(a); //要实例化 
    cout << "计算长方形面积（输入长和宽）" << endl;
    cin >> b >> c;
    Rectangle H(b, c); //要实例化 
    return 0;
}
Rectangle::Rectangle(double x)
{
    double area = x * x;
    cout << "正方形面积为：" << endl;
    cout << area << endl;
}
Rectangle::Rectangle(double b, double c)
{
    double area = c * b;
    cout << "长方形面积为：" << endl;
    cout << area << endl;
}