OKLAHOMA CITY--(BUSINESS WIRE)--Sonic Corp. (NASDAQ:SONC), the nation's largest chain of drive-in restaurants, today announced that its Board of Directors has declared a regular quarterly cash dividend of $0.09 per share of common stock. The dividend is payable on August 21, 2015 to shareholders of record as of the close of business on August 12, 2015. The future declaration of quarterly dividends and the establishment of future record and payment dates are subject to the final determination of