Returning Integer Value in Obj-C String

I'm pretty new to Objective-C, switching over from C++, so excuse my stupid question.

I know with NSLogs and what not NSLog(@"%d is the index",i); is valid syntax开发者_Go百科. What is the reason that this: return [UIImage imageNamed:@"cover_%d.jpg", value]; isn't?

I get an error in my IDE telling me that I have too many arguments, i.e. the integer is never being used. How do I get the integer to reflect in a non-log situation?

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[UIImage imageNamed:[NSString stringWithFormat:@"cover_%d.jpg", value]];

The string literal syntax doesn't support formats.

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The %d (etc.) syntax is a specific convention used by particular functions like NSLog, it's not a general purpose Objective-C operation that you can expect to work with arbitrary method invocations.

Fortunately, another method that supports the %-substitutions is NSSTRing -stringWithFormat:. You use that method to create a string using the substitutions, then use that string as desired. For example:

NSString *imgName = [NSString stringWithFormat:@"cover_%d.jpg", value];
return [UIImage imageNamed:imgName];

(you could also combine these two lines into a single expression, eliminating the temporary imgName variable)