how can i search textbox control on the current form in C#.net windows application ??

please refer the below code ...

private TextBox GetTextBox()
        {
            TextBox txtPasskey = new TextBox();
            txtPasskey.Name = "txtPasskey";
            txtPasskey.MaxLength = 8;
            txtPasskey.PasswordChar = '*';
            txtPasskey.TextAlign = HorizontalAlignment.Left;
            txtPasskey.Location = new Point(200, 200);
            txtPasskey.TextChanged += new EventHandler(this.txtPasskey_TextChanged);
            txtPasskey.Validating += new CancelEventHandler(this.txtPasskey_Validating);
            return txtPasskey;
        }

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now how can i find above textbox(txtPasskey) without linq ??

Why wouldn't you use LINQ ? If you really not want to do that, you'll need to implement a loop over all your controls

Example without linq

foreach (Control con in mainForm.Controls)
    {
        if ( control is Textbox  && control.Name = ""YourTextBox")
                 // now you have your textbox
    }


See also: http://www.dotnetperls.com/query-windows-forms

You can also use the Old Way ;-)

TextBox MyTextBox = control.FindControl("YourTextBox") as TextBox;