You are not changing the strings. NSString
objects are immutable, you either have to assign the result:
word2 = [word2 stringByAppendingString:@"0"];
or use NSMutableString
and appendString:
[word2 appendString:@"0"];
You also have to reverse your logic, as "append" means "add to the end".
append |əˈpɛnd| verb [ with obj. ] add (something) to the end of a written document: the results of the survey are appended to this chapter.