目标C-使用stringByAppendingFormat的多行字符串

Question

I'm having an issue with the following code. I want the resultant multiLineTitle to look like this

Each
Word
Should 
Have 
Its 
Own 
Line

But when I run this program, multiLineTitle ends up null . Can anyone spot the issue?

    NSString *title = "Each Word Should Have Its Own Line";
    NSString *multiLineTitle;

    NSArray *words = [title componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    words = [words filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF != ''"]];

    for (int len = 0; len < [words count]; len++){
        multiLineTitle = [multiLineTitle stringByAppendingFormat:@"%@ \n", words[len]];

    }

Answer 1

assign empty string to multiLineTitle or allocate memory for multiLineTitle.

NSString *multiLineTitle = @"";

or

NSString *multiLineTitle = [[NSString alloc]init];

Answer 2

solution....
NSString *title =@"Each Word Should Have Its Own Line";
    NSMutableString *multiLineTitle =[[NSMutableString alloc] init];

    NSArray *words = [title componentsSeparatedByCharactersInSet:[NSCharacterSet whitespaceCharacterSet]];
    words = [words filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"SELF != ''"]];

    for (int len = 0; len < [words count]; len++){
     [multiLineTitle appendFormat:@"%@\n",[words objectAtIndex:len]];

    }
    NSLog(@"multiLineTitle:%@",multiLineTitle);




ans:
multiLineTitle:Each
Word
Should
Have
Its
Own
Line