Format specifiers are the percent character, followed by a letter, such as %d or %f that tell NSLog or printf() to print the value or result of a variable, value, and/or expression.
Here is a list of C format specifiers:
Just think of them as types of placeholders, each designed to represent a different value.
Kevin M.
/ September 17, 2012There’s also %@ to be used when you want to display an object in an NSLog. Secretly, it’s running the -description method on an object, which returns a string. When you’re beginning, you’ll probably use this to print NSString ‘s.
http://developer.apple.com/library/mac/#documentation/cocoa/conceptual/Strings/Articles/formatSpecifiers.html