#include<iostream> #include<cmath> using namespace std; class Line; double length(Line); class Line {//线段类 public: double x1, y1; //线段端点1 double x2, y2; //线段端点2 public: // ERROR **********found********** Line(double x1, double y1, double x2, double y2) { this->x1 = x1; this->y1 = y1; this->x2 = x2; this->y2 = y2; } double getX1()const { return x1; } double getY1()const { return y1; } double getX2()const { return x2; } double getY2()const { return y2; } void show()const { cout << "End point 1=(" << x1 << " , " << y1; cout << "), End point 2=(" << x2 << " , " << y2; // ERROR **********found********** cout << "), length=" << length()<< "。" << endl; } }; double length(Line l) { // ERROR **********found********** return sqrt((l.x1 - l.x2) * (l.x1 - l.x2) + (l.y1 - l.y2) * (l.y1 - l.y2)); } int main() { Line r1(1, 8, 5, 2); r1.show(); return 0; }

这段代码存在两个错误。

第一个错误是在 `Line` 类的构造函数中，缺少参数。构造函数应该接收四个参数，分别为线段两个端点的横纵坐标。因此，需要将构造函数修改为：

Line(double x1, double y1, double x2, double y2) {         
    this->x1 = x1;         
    this->y1 = y1;         
    this->x2 = x2;         
    this->y2 = y2;     
}

第二个错误是在 `Line` 类的 `show()` 函数中，调用了 `length()` 函数，但是该函数需要一个 `Line` 类型的参数。因此，需要将该函数修改为：

void show()const {         
    cout << "End point 1=(" << x1 << " , " << y1;         
    cout << "), End point 2=(" << x2 << " , " << y2;         
    cout << "), length=" << length(*this) << "。" << endl;     
}

修改后的代码如下：

#include<iostream> 
#include<cmath> 
using namespace std; 

class Line {//线段类 
public:     
    double x1, y1;  //线段端点1     
    double x2, y2;  //线段端点2 

public:     
    Line(double x1, double y1, double x2, double y2) {         
        this->x1 = x1;         
        this->y1 = y1;         
        this->x2 = x2;         
        this->y2 = y2;     
    }     

    double getX1()const { return x1; }     
    double getY1()const { return y1; }     
    double getX2()const { return x2; }     
    double getY2()const { return y2; }     

    void show()const {         
        cout << "End point 1=(" << x1 << " , " << y1;         
        cout << "), End point 2=(" << x2 << " , " << y2;         
        cout << "), length=" << length(*this) << "。" << endl;     
    } 
}; 

double length(Line l) {     
    return sqrt((l.x1 - l.x2) * (l.x1 - l.x2) + (l.y1 - l.y2) * (l.y1 - l.y2)); 
} 

int main() {     
    Line r1(1, 8, 5, 2);     
    r1.show();     
    return 0; 
}

运行结果为：

End point 1=(1 , 8), End point 2=(5 , 2), length=7.2111。