int num = some numerical value;
status.Text = "Successfully Deleted"+ " " + num + " " + "Files";

int num = 5;
status.Text = String.Format("Successfully Deleted {0} Files", num);

int num = 5;
StringBuilder sb = new StringBuilder();
sb.AppendFormat("Successfully Deleted {0} Files", num);
status.Text = sb.ToString();

status.Text = "Successfully Deleted " + num + " Files";

public static string SurroundWithSpaces(this object o)
{
    return " " + o + " ";
}
status.Text = "Successfully Deleted" + num.SurroundWithSpaces() + "Files";