C#-Code

using System;
using System.Collections.Generic;
using System.Drawing;
using System.Windows.Forms;

namespace count_area_train_your_programmer
{
    public partial class Form1 : Form
    {
        int counter = 0;

        static Random rnd = new Random((int)DateTime.Now.Ticks);
        int lines = 1;
        int area_count = 0;
        int width = 0;
        int height = 0;
        Color pencolor = Color.Red;

        //-------------------------------------

        public Form1()
        {
            InitializeComponent();
            pictureBox_canvas.Image = new Bitmap(pictureBox_canvas.Width, pictureBox_canvas.Height);
            width = pictureBox_canvas.Width;
            height = pictureBox_canvas.Height;
        }

        //-------------------------------------

        private void button_draw_Click(object sender, EventArgs e)
        {
            area_count = 0;
            Color color = new Color();
            Point pos1 = new Point(0, 0);
            Point pos2 = new Point(0, 0);

            label_areacount.Text = "";
            pictureBox_canvas.Image.Dispose();
            pictureBox_canvas.Image = new Bitmap(pictureBox_canvas.Width, pictureBox_canvas.Height);
            pictureBox_canvas.Refresh();

            Pen pen = new Pen(pencolor, 2);
            Image image = pictureBox_canvas.Image;

            for (int i = 0; i < lines; i++)
            {
                Get_random_Points(ref pos1);
                Get_random_Points(ref pos2);

                while (pos1.X == pos2.X || pos1.Y == pos2.Y)
                {
                    Get_random_Points(ref pos2);
                }



                using (Graphics grahpics = Graphics.FromImage(image))
                {
                    grahpics.DrawLine(pen, pos1, pos2);
                }
                pictureBox_canvas.Image = image;
            }

            for (int i = 0; i < width-1; i++)
            {
                for (int f = 0; f < height-1; f++)
                {
                    color = GetColorAt(i, f);

                    if (color.A == 0)
                    {
                        Check_pixels(i, f);
                    }
                }
            }
            label_areacount.Text = area_count.ToString();
        }

        //-------------------------------------

        public void Get_random_Points(ref Point pos)
        {
            counter = rnd.Next(0, 4);
            switch (counter)
            {
                case 0:
                    pos.X = rnd.Next(0, width+1);
                    pos.Y = -1;
                    break;

                case 1:
                    pos.X = rnd.Next(0, width+1);
                    pos.Y = height+1;
                    break;

                case 2:
                    pos.Y = rnd.Next(0, height+1);
                    pos.X = -1;
                    break;

                case 3:
                    pos.Y = rnd.Next(0, height+1);
                    pos.X = width+1;
                    break;
            }
        }

        //-------------------------------------

        public Color GetColorAt(int x, int y)
        {
            return ((Bitmap)pictureBox_canvas.Image).GetPixel(x, y);
        }

        //-------------------------------------

        public void Check_pixels(int x, int y)
        {
            Color color = new Color();
            Image image = pictureBox_canvas.Image;
            List<Point> points = new List<Point>();
            points.Add(new Point(x, y));
            area_count++;

            while (points.Count != 0)
            {
                foreach(Point pnt in points)
                {
                    color = GetColorAt(pnt.X, pnt.Y);
                    if (color.A == 0)
                    {
                        using (Graphics graph = Graphics.FromImage(image))
                        {
                            Brush aBrush = (Brush)Brushes.Black;
                            graph.FillRectangle(aBrush, pnt.X, pnt.Y, 1, 1);
                        }
                    }
                }

                Direction_Check(points, color, -1, 0);
                Direction_Check(points, color, 1, 0);
                Direction_Check(points, color, 0, 1);
                Direction_Check(points, color, 0, -1);
                points.RemoveAt(0);               
            }
            pictureBox_canvas.Image = image;           
        }

        //-------------------------------------

        public void Direction_Check(List<Point>points, Color color, int to_x, int to_y)
        {
            if (points[0].X + to_x >= 0 && points[0].Y + to_y >= 0 &&
                points[0].X + to_x <= width-1 && points[0].Y + to_y <= height-1)
            {
                color = GetColorAt(points[0].X + to_x, points[0].Y + to_y);

                if (color.A == 0 && color.R == 0 && color.G == 0 && color.B == 0)
                {
                    points.Add(new Point(points[0].X + to_x, points[0].Y + to_y));
                }
            }
        }

        //-------------------------------------

        private void textBox_linecount_TextChanged(object sender, EventArgs e)
        {
            int.TryParse(textBox_linecount.Text, out lines);
            label_linecount.Text = lines.ToString();
        }
    }
}