C ++错误：没有在范围内声明； 会员功能

Question

I have a an error for 'Result Vector' was not declared in this scope. I am not sure of where to or how to declare this? The intention of the Result Vector is the show the result of adding the X's of vectors and the Y's of each vector and then return result_vector

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

class vector{
private:
    double x;
    double y;
public:
    //Constructor - default
    vector() : x(0), y(0) {}
    //Constructor - Custom
    vector(double xx, double yy) : x(xx), y(yy) {}
    //Get X & Y Coordinates
    double get_x() { return x;
    }
    double get_y() { return y;
    }
    //Set X & Y Coordinates
    void set_x( double xx) { x = xx;
    }
    void set_y( double yy) { y = yy;
    }
    //Adding Vectors
    vector add_vector( vector v1, vector v2){ 
        result_vector.x = v1.x + v2.x;
        result_vector.y = v1.y + v2.y;
        return result_vector; 
    }
    //Subtracting Vectorsed
    vector subtract_vector( vector v1, vector v2){
        result_vector.x = v1.x - v2.x;
        result_vector.y = v1.y - v2.y;
        return result_vector;
    }
};

int main() {
    //Default
    vector test;
    cout <<"Default \n" test.get_x().get_y() << "\n";
    //Customer
    vector test2(10, 12);
    cout <<"Custom \n" test2.get_x().get_y() << "\n";
    //Adding
    vector add = vector.add_vector(vector test1&, vector test2&);
    cout <<"Adding \n" add.get_x().get_y() <<"\n";
    //Subtracting
    vector sub = vector.subtract_vector(vector test1&, vector test2&);
    cout <<"Subtracting \n" sub.get_x().get_y() <<"\n";

    return 0;


}

Answer 1

You haven't declared result_vector it doesn't exist, hence the error.

Also, you're using namespace std; and you've named a class vector .
therefore the reference to vector is ambiguous.

Your code has several other errors, I suggest you use a debugger and go through the errors

Answer 2

The error is self explanatory.

• You need to declare result_vector before its first use.
• You can't pass the class name along with object name as arguments.
• Assuming this statement cout <<"Default \\n" test.get_x().get_y() << "\\n"; is supposed to print the x and y values of vector, you will have to call get_x() and get_y() separately.

• Also as mentioned by Andreas DM you can't use using namespace std; because it conflicts with the existing class vector.vector class after making the corrections

   #include <iostream> #include <vector> class vector{ private: double x; double y; public: //Constructor - default vector() : x(0), y(0) {} //Constructor - Custom vector(double xx, double yy) : x(xx), y(yy) {} //Get X & Y Coordinates double get_x() { return x; } double get_y() { return y; } //Set X & Y Coordinates void set_x( double xx) { x = xx; } void set_y( double yy) { y = yy; } //Adding Vectors vector add_vector( vector v2){ vector result_vector; result_vector.x = x + v2.x; result_vector.y = y + v2.y; return result_vector; } //Subtracting Vectorsed vector subtract_vector( vector v2){ vector result_vector; result_vector.x = x - v2.x; result_vector.y = y - v2.y; return result_vector; } }; int main() { //Default vector test; std::cout <<"Default \\n" <<test.get_x()<<test.get_y() << "\\n"; //Customer vector test2(10, 12); std::cout <<"Custom \\n" <<test2.get_x()<<test2.get_y() << "\\n"; //Adding vector add; add = test.add_vector(test2); std::cout <<"Adding \\n" <<add.get_x()<<add.get_y() <<"\\n"; //Subtracting vector sub ; sub = test.subtract_vector(test2); std::cout <<"Subtracting \\n"<< sub.get_x()<<sub.get_y() <<"\\n"; return 0; } 

Answer 3

Before you use a variable, you have to it, so that the compiler knows it exits. In C++ this is required (some languages, like Python, don't require it), and so declare result_vector first before you use it ( vector result_vector; )