#include <graphics.h>
#include <iostream>
using namespace std;
class line
{
protected:
    int x1, x2, y1, y2;

public:
    void drawl()
    {
        float x, y, dx, dy, step;
        int i;
        dx = abs(x2 - x1);
        dy = abs(y2 - y1);
        if (dx >= dy)
        {
            step = dx;
        }
        else
            step = dy;
        dx = (x2 - x1) / step;
        dy = (y2 - y1) / step;
        x = x1 + 0.5;
        y = y1 + 0.5;
        i = 1;
        while (i <= step)
        {
            putpixel(x, y, 15);
            x = x + dx;
            y = y + dy;
            i = i + 1;
        }
        putpixel(x, y, 15);
    }
};

class polygon : public line
{
    int a[10][2];

public:
    void setpts(int i)
    {
        int j, k;
        for (j = 0; j < i; j++)
        {
            cout << "Enter the coordinate x" << j << " ";
            cin >> a[j][0];
            cout << "Enter the coordinate y" << j << " ";
            cin >> a[j][1];
        }
    }
    void drawpoly(int i)
    {
        int j;
        x1 = a[0][0];
        y1 = a[0][1];
        x2 = a[1][0];
        y2 = a[1][1];
        line::drawl();
        for (j = 1; j < i - 1; j++)
        {
            x1 = a[j][0];
            y1 = a[j][1];
            x2 = a[j + 1][0];
            y2 = a[j + 1][1];
            line::drawl();
        }
        x1 = a[j][0];
        y1 = a[j][1];
        x2 = a[0][0];
        y2 = a[0][1];
        line::drawl();
    }
};

int main()
{
    int n, gd = DETECT, gm;
    cout << "Enter the number of sides of polygon ";
    cin >> n;
    polygon P;
    P.setpts(n);
    initgraph(&gd, &gm, NULL);
    P.drawpoly(n);
    delay(5000);
    return 0;
}

kodingwindow@kw:~$ g++ kw.cpp -lgraph
kodingwindow@kw:~$ ./a.out
Enter the number of sides of polygon 6
Enter the coordinate x0 100
Enter the coordinate y0 100
Enter the coordinate x1 150
Enter the coordinate y1 150
Enter the coordinate x2 150
Enter the coordinate y2 200
Enter the coordinate x3 100
Enter the coordinate y3 250
Enter the coordinate x4 50
Enter the coordinate y4 200
Enter the coordinate x5 50
Enter the coordinate y5 150