Creating a Class with 2 double values in C++

Question

In C++ I am trying to create a class Point2D that contains two double values. All data members and functions should be public.

For Public Members there should be

• double x
• double y

For Constructors

• the default constructor should initialize x and y to 0.0

• Point2D(double in_x, double in_y)

  • sets x and y to in_x and in_y

For non-member Functions

• void GetResult(Point2D p1, Point2D p2)

  • Prints x and y values for both

This is the code I have so far, can somebody please point out my errors?

Point2D.h

#ifndef POINT2D_H
#define POINT2D_H

class Point2D
{
public:
    double x;
    double y;

Point2D();
Point2D(double,double);

};

void GetResult(Point2D, Point2D);

#endif

Point2D.cpp

#include "Point2D.h"
#include <iostream>
using namespace std;

Point2D::Point2D()
{
    x = 0.0;
    y = 0.0;
}

Point2D::P1(double in_x, double in_y)
{
    x = in_x;
    y = in_y;
}

Point2D::P2(double in_x, double in_y)
{
    x = in_x;
    y = in_y;
}

void GetResult(Point2D P1, Point2D P2)
{
    cout << P1.x << " " << P1.y << endl;
    cout << P2.x << " " << P2.y << endl;
}

TestCheckPoint1.cpp

#include <iostream>
#include "Point2D.h"
using namespace std;

int main()
{
    Point2D Point1;
    Point1.x = 1.0;
    Point1.y= 2.0;

    Point2D Point2;
    Point2.x= 1.0;
    Point1.y= 2.0;

    GetResult(Point1, Point2);
}

Answer 1

You are close, but it is clear you have a bit of misunderstanding about overloaded constructors and declaring instances of your class. For starters, you don't need the functions:

Point2D::P1(double in_x, double in_y)
{
    x = in_x;
    y = in_y;
}

Point2D::P2(double in_x, double in_y)
{
    x = in_x;
    y = in_y;
}

You simply need a single constructor for your Point2D class that takes two double values, e.g.

Point2D::Point2D(double in_x, double in_y)
{
    x = in_x;
    y = in_y;
}

Then in main() you need to declare and initialize default constuct two-instances of class Point2D providing the desired values to x and y before calling GetResult, e.g.

#include <iostream>
#include "Point2D.h"
using namespace std;

int main()
{
    Point2D Point1 (1.0, 2.0);
    Point2D Point2 (1.0, 2.0);

    GetResult(Point1, Point2);
}

(note: You can provide an initializer lists that allow initialization of the class members, see Constructors and member initializer lists. You could provide an initializer list for your constructor with, e.g. Point2D() : x(0), y(0) {}; and the overload Point2D(double, double);. Your constructor definition would simply be Point2D::Point2D(double in_x, double in_y) : x(in_x), y(in_y) {} and the compiler would initialize x, y to 0, 0 if created with Point2D Point1; or set x, y to values provided as Point2D Point2 (1.0, 2.0);)

You did a very good job including the Header Guards around the contents of Point2D.h to prevent multiple inclusion if included in more than one file. The complete header and source files for Point2D could be:

#ifndef POINT2D_H
#define POINT2D_H

class Point2D
{
public:
    double x;
    double y;

    Point2D();
    Point2D(double,double);

};

void GetResult(Point2D, Point2D);

#endif

and

#include "Point2D.h"
#include <iostream>
using namespace std;

Point2D::Point2D()
{
    x = 0.0;
    y = 0.0;
}

Point2D::Point2D(double in_x, double in_y)
{
    x = in_x;
    y = in_y;
}

void GetResult(Point2D P1, Point2D P2)
{
    cout << P1.x << " " << P1.y << endl;
    cout << P2.x << " " << P2.y << endl;
}

Example Use/Output

Compiling and running would result in:

$ ./bin/TestCheckPoint1
1 2
1 2

Note: there is no need to using namespace std; in main() at all, and you really shouldn't include the entire standard namespace anywhere. Simply remove both calls and add std:: to your two cout calls and two calls to endl (or just use '\n' instead of std::endl;). See Why is “using namespace std;” considered bad practice?

Instead simply use:

void GetResult(Point2D P1, Point2D P2)
{
    std::cout << P1.x << " " << P1.y << '\n';
    std::cout << P2.x << " " << P2.y << '\n';
}

Look things over and let me know if you have further questions.