point-distance

0_point.java

public class Point {
    private double x;
    private double y;

    public Point(double x, double y) {
        this.x = x;
        this.y = y;
    }

    public double distance(Point that) {
        double xdist = this.x - that.x; 
        double ydist = this.y - that.y;
        double distance = Math.sqrt( (xdist*xdist) + (ydist*ydist) );
        return distance;
    }

    //imagine getX, getY, setX, setY functions here

}

1_main.java

//// in some main file, imagine using it like so:

public class Main {

    public static void main {

        Point p1 = new Point(1, 2);
        Point p2 = new Point(10, -2);

        int distance = p1.distance(p2);
    }

}

2_distance.h

#ifndef __DISTANCE_H__
#define __DISTANCE_H__

/* Let's create the simplest struct we could want, a pair of numbers */
struct point {
    double x;
    double y;
};

/* now let's define a distance function  that takes two struct points*/
double distance(struct point p1, struct point p2); 

/* just for fun, let's define a distance function that takes 4 doubles directly */
double distance(double x1, double y1, double x2, double y2); 

#endif

3_distance.c

#include "distance.h"
#include <math.h> /* need it for the sqrt function */

double distance(struct point p1, struct point p2) {

    double xdist = p1.x - p2.x; 
    double ydist = p1.y - p2.y;

    double distance = sqrt( (xdist*xdist) + (ydist*ydist) );

    return distance;
}

double distance(double x1, double y1, double x2, double y2) {

    double xdist = x1 - x2; 
    double ydist = y1 - y2;

    double distance = sqrt( (xdist*xdist) + (ydist*ydist) );

    return distance;
}

4_main.c

#include "distance.h"

int main(int argc, char **argv) {

    struct point p1;
    p1.x = 1;
    p1.y = 2;

    struct point p2;
    p2.x = 10;
    p2.y = -2;

    double dist = distance(p1, p2);

    /* here's an alternate way of doing it, without using structs */
    double x1 = 1;
    double y1 = 2;
    double x2 = 10;
    double y2 = -2;

    dist = distance(1, 2, 10, -2);

    return 0;
}