NSInteger不是对象, 转换为long匹配64位系统, 再组成字符串(%ld).

NSString *inStr = [NSString stringWithFormat: @"%ld", (long)month];

Note that on 64-bit processors, such as the new A7 chip, if your app is compiled for 64-bit, an NSInteger is actually a long, not an int. Doing the cast, (int)month would be destructive on 64-bit platforms for the generic case. If targeting Apple platforms exclusively, something similar that will work with both int and long – e.g. long.