How to show images from folder into Picture box?

using System.Text;
using System.Windows.Forms;
using System.Collections;

namespace WindowsFormsApplication15
{
    public partial class Form1 : Form
    {
        ArrayList alist = new ArrayList();
        int i = 0;
        int filecount = 0;

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            //Specify Source folder path here
            System.IO.DirectoryInfo inputDir = new System.IO.DirectoryInfo("D:\\images");
            try
            {
                if ((inputDir.Exists))
                {

                    //Get Each jpg files from a source folder and stored in the arraylist
                    System.IO.FileInfo file = null;
                    foreach (System.IO.FileInfo eachfile in inputDir.GetFiles())
                    {
                        file = eachfile;
                        if (file.Extension.ToLower() == ".jpg")
                        {
                            alist.Add(file.FullName);
                            //Store file count here 
                            filecount = filecount + 1;
                        }
                    }
                    //Initally show first image in the picture box
                    pictureBox1.Image = Image.FromFile(alist[0].ToString()); ;
                    i = 0;
                }
            }
            catch (Exception ex)
            {
              
            }
        }

        private void btnNext_Click(object sender, EventArgs e)
        {
            //check next postion image is have or not
            if (i + 1 < filecount)
            {
                pictureBox1.Image = Image.FromFile(alist[i + 1].ToString()) ;
                i = i + 1;
            }
        }

        private void btnPrevious_Click(object sender, EventArgs e)
        {
            //check previous postion image is have or not
            if (i - 1 >= 0)
            {
                pictureBox1.Image = Image.FromFile(alist[i-1].ToString()) ;
                i = i - 1 ;
            }
        }
       
    }
}