drawing line without using drawLine method in c#

Here is my code and I want to implement DDA algorithm without using drawLine method in c# . I tried to use PutPixel method but it did not work . There is nothing in my window. Is there any way to draw line without using drawLine method in c# ?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace Proje1B
{
public partial class Form1 : Form
{
    public Boolean drawingFlag = false;
    public Point ilk, ikinci;

    Graphics grafik;

    public Form1()
    {
        InitializeComponent();
    }

    private void Form1_Paint(object sender, PaintEventArgs e)
    {
        grafik = e.Graphics;

        DDACiz(ilk.X, ilk.Y, ikinci.X, ikinci.Y, grafik, Color.DarkRed);


    }
    private void Form1_MouseDown(object sender, MouseEventArgs e)
    {
        if (!drawingFlag)
        {
            drawingFlag = true;
            ilk = e.Location;
        }
    }

    private void Form1_MouseUp(object sender, MouseEventArgs e)
    {
        drawingFlag = false;
    }
    private void Form1_MouseMove(object sender, MouseEventArgs e)
    {
        if (drawingFlag)
        {
            ikinci = e.Location;
            Invalidate();
        }
    }
    void PutPixel(Graphics g, int x, int y, Color c) // sadece bir pixel icin
    {
        System.Drawing.Bitmap bm = new System.Drawing.Bitmap(10, 10);
        bm.SetPixel(0, 0, Color.DarkRed);
        g.DrawImageUnscaled(bm, x, y);
    }

    void DDACiz(int x1, int y1, int x2, int y2,Graphics grafik, Color renk)
    {

        int PikselSayisi;

        int dx, dy;
        float x, xFark;
        float y, yFark;

        dx = x2 - x1;
        dy = y2 - y1;

        PikselSayisi = Math.Abs(dx) > Math.Abs(dy) ? Math.Abs(dx) : Math.Abs(dy);

        xFark = (float)dx / (float)PikselSayisi;
        yFark = (float)dy / (float)PikselSayisi;

        x = (float)x1;
        y = (float)y1;

        while (PikselSayisi!=0)
        {
           PutPixel(grafik,(int)Math.Floor(x + 0.5F),(int) Math.Floor(y + 0.5f),renk);
            x += xFark;
            y += yFark;
            PikselSayisi--;
        }
    }
}
}