使用NSString和NSMutableString ：
NSString *simpleString = @"This is a simple string";
NSString *anotherString =
[NSString stringWithString:@"This is another simple string"];
NSString *oneMorestring =
[[NSString alloc] initWithString:@"One more!"];
NSMutableString *mutableOne =
[NSMutableString stringWithString:@"Mutable String"];
NSMutableString *anotherMutableOne =
[[NSMutableString alloc] initWithString:@"A retained one"];
NSMutableString *thirdMutableOne =
[NSMutableString stringWithString:simpleString];