Shares of drive-in fast-food restaurant chain Sonic (NASDAQ:SONC) fell yesterday, after first-quarter earnings came in below expectations. Foolish investors may want to consider taking advantage of the downturn, since Sonic has a whole menu of appealing investment characteristics.

The dip in earnings for the quarter was due to increased interest expense and debt refinancing charges. The company refinanced a bank loan and took on additional debt to repurchase more than $400 million in shares, or 20% of outstanding stock. The effects are expected to carry over into the second quarter, and they could increase interest expense for some time. Nonetheless, Sonic has a solid historical track record of growth, with continued bright prospects.

Earnings and sales have grown right around 17% each year for the past five years, and they've been consistent on an annual basis. Operating cash flow has grown close to 20% over the past couple of years, exceeding reported net income by a wide margin. Sonic doesn't really need any debt, since it generates more capital internally than it spends to maintain and grow its store base. That's primarily because more than 80% of the store base is franchised, leaving spending requirements to outside parties, and generating subsequent high-margin franchise royalties.

Management targets annual earnings growth of 18%, predicting further growth in the current 33 states where stores are located. With only about 3,200 locations currently, Sonic should be able to continue growing in the double digits for the foreseeable future. As a comparison, McDonald's (NYSE:MCD) operates more than 30,000 stores globally, while Yum! Brands (NYSE:YUM) operates more than 34,000 stores. I don't know whether the drive-in concept can experience similar levels of success overseas, but the figures demonstrate there is ample room for more Sonics throughout the world.

Domestically, the drive-in concept does offer some form of differentiation in the crowded fast-food realm of dining out, which also includes Jack in the Box (NYSE:JBX) and Wendy's (NYSE:WEN). Sonic also has a reputation for a loyal customer base that either likes the nostalgic drive-in experience, enjoys the convenience of eating in their automobiles, or keeps coming back to try the new menu items Sonic frequently introduces.

In any case, Sonic has put together a solid string of top- and bottom-line growth, and it generates decent levels of cash flow. Fools looking for restaurant exposure in their portfolios may want to consider a bite out of Sonic, since its future outlook also looks tasty.

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Fool contributor Ryan Fuhrmann is long shares of Mickey D's but has no financial interest in any other company mentioned. Feel free to email him with feedback or to discuss any companies mentioned further. The Fool has an ironclad disclosure policy.