NSString *s1 = @"three";
NSString *s2 = @"two";
NSMutableString *s3 = [NSMutableString stringWithFormat:@"%@%@%@", s1, @", ",
                       s2];
[s3 appendString: @", one"];
NSString *sGo = [NSString stringWithFormat:@"%@%@%@", s3, @", ", @"go!"];

//sGo is "three, two, one, go!"