如何检测字符是大写还是小写？

BOOL isUppercase = [[NSCharacterSet uppercaseLetterCharacterSet] characterIsMember:[s characterAtIndex:0]];

unichar ch = [@\"This is my String\" characterAtIndex:0];

if (ch >= \'A\' && ch <= \'Z\') {
    // upper case
} else if (ch >= \'a\' && ch <= \'z\') {
   // lower case
}

NSString *firstChar = [NSString stringWithFormat:@\"%c\", [@\"This is my String\" characterAtIndex:0]];

BOOL isUpperCase = [firstChar isEqualToString:[firstChar uppercaseString]];