After flitting between tiny gains and losses, stocks closed mostly lower, a peaceful end to the most volatile month in nearly two years. Investors seemed unsure how to react to recent statements by Fed officials about when the central bank might end its bond buying. Mixed economic news — an index of consumer confidence was up but a gauge of business activity in the Chicago area fell — also added to uncertainty. BlackBerry plunged after the smartphone maker posted a loss in the first quarter and warned of future losses. Accenture also fell after the firm cut its revenue and profit outlook. Revenue was hurt by lower demand in Europe.