C Encapsulation

point.h 

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struct Point;

struct Point* makePoint(double x, double y);

double getDistance(struct Point *p1, struct Point *p2);

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point.c

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/* point.c */

#include "point.h"

#include <stdlib.h>

#include <math.h>

struct Point {

    double x, y;

}

struct Point* makePoint(double x, double y) {

    struct Point* p = malloc(sizeof(struct Point));

    p->x = x;

    p->y = y;

    return p;

}

double getDistance(struct Point* p1, struct Point *p2) {

    double dx = p1->x - p2->x;

    double dy = p1->y - p2->y;

    return sqrt(dx*dx + dy*dy);

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Compare C++

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point.h

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class Point {

public:

    Point(double x, double y);

    double getDistance(const Point& p) const;

private:

    double x;

    double y;

}

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point.cc

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#include "point.h"

#include <math.h>

Point::Point(double x, double y): x(x), y(y) {}

double Point::getDistance(const Point& p) const {

    double dx = x - p.x;

    double dy = y - p.y;

    return sqrt(dx*dx + dy*dy);

}

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