1:

if (myTextBox.Text.Contains("a"))    // usw.                    

1:
2:
3:
4:
5:
6:
7:
8:
9:
10:
11:
12:
13:
14:
15:
16:
17:
18:
19:
20:
21:
22:
23:
24:
25:
26:
27:
28:
29:
30:
31:
32:
33:
34:
35:
36:
37:
38:
39:
40:
41:
42:
43:
44:
45:
46:
47:
48:
49:
50:
51:
52:
53:
54:
55:
56:
57:
58:
59:
60:
61:
62:
63:
64:
65:
66:
67:
68:
69:
70:
71:
72:
73:
74:
75:
76:
77:
78:
79:
80:
81:
82:

// GListBoxItem class 
    public class GListBoxItem
    {
        private string _myText;
        private int _myImageIndex;
        // properties 
        public string Text
        {
            get { return _myText; }
            set { _myText = value; }
        }
        public int ImageIndex
        {
            get { return _myImageIndex; }
            set { _myImageIndex = value; }
        }
        //constructor
        public GListBoxItem(string text, int index)
        {
            _myText = text;
            _myImageIndex = index;
        }
        public GListBoxItem(string text) : this(text, -1) { }
        public GListBoxItem() : this("") { }
        public override string ToString()
        {
            return _myText;
        }
    }//End of GListBoxItem class

    // GListBox class 
    public class GListBox : ListBox
    {
        private ImageList _myImageList = new ImageList();
        public ImageList ImageList
        {
            get { return _myImageList; }
            set { _myImageList = value; }
        }
        public GListBox()
        {
            // Set owner draw mode
            this.DrawMode = DrawMode.OwnerDrawFixed;
        }
        protected override void OnDrawItem(System.Windows.Forms.DrawItemEventArgs e)
        {
            e.DrawBackground();
            e.DrawFocusRectangle();
            GListBoxItem item = new GListBoxItem();
            Rectangle bounds = e.Bounds;
            Size imageSize = _myImageList.ImageSize;
            try
            {
                item = (GListBoxItem)Items[e.Index];
                if (item.ImageIndex != -1)
                {
                    ImageList.Draw(e.Graphics, bounds.Left, bounds.Top, item.ImageIndex);
                    e.Graphics.DrawString(item.Text, e.Font, new SolidBrush(e.ForeColor),
                        bounds.Left + imageSize.Width, bounds.Top);
                }
                else
                {
                    e.Graphics.DrawString(item.Text, e.Font, new SolidBrush(e.ForeColor),
                        bounds.Left, bounds.Top);
                }
            }
            catch
            {
                if (e.Index != -1)
                {
                    e.Graphics.DrawString(Items[e.Index].ToString(), e.Font,
                        new SolidBrush(e.ForeColor), bounds.Left, bounds.Top);
                }
                else
                {
                    e.Graphics.DrawString(Text, e.Font, new SolidBrush(e.ForeColor),
                        bounds.Left, bounds.Top);
                }
            }
            base.OnDrawItem(e);
        }
    }