private void txtShortcut_KeyDown(object sender, KeyEventArgs e)
    {
        if (e.Shift || e.Control || e.Alt)
        {
            txtShortcut.Text = (e.Shift.ToString() + e.Control.ToString() + e.Alt.ToString() + e.KeyCode.ToString());

        }
    }

string s = (e.Shift ? "[Shift]+" : "") + (e.Control ? "[Ctrl]+" : "")
           + (e.Alt ? "[Alt]+" : "") + e.KeyCode;

txtShortcut.Text = (e.Shift? "Shift ": "") + (e.Control? "Control ": "") + (e.Alt? "Alt ": "")  + e.KeyCode.ToString());

txtShortcut.Text = (e.Shift ? "[Shift]" : string.Empty) +
                   (e.Control ? "[Ctrl]" : string.Empty) + ...;

<someBool> ? <ifTrue> : <ifFalse>

var kc = new KeysConverter();
var result = kc.ConvertToString(e.KeyCode);

var keys = (e.Shift ? "[Shift]+" : string.Empty)
             + (e.Control ? "[Ctrl]+" : string.Empty)
             + (e.Alt ? "[Alt]+" : string.Empty)
             + e.KeyCode;