date code and string reverse

[Dan Holmes]

I have a need to reverse a date to show as a "date code". For example
today, 090507 would be coded as 905070 (reversing the parts of the date.

This is what i have but there has to be a better way.

DateTime d = DateTime.Now;
string datecodemonth = d.ToString("MM" );
datecodemonth = datecodemonth[1] + datecodemonth[0];
string datecodeday = d.ToString("dd" );
datecodeday = datecodeday[1] + datecodeday[0];
string datecodeyear = d.ToString("yy" );
datecodeyear = datecodeyear[1] + datecodeyear[0];
string datecode = datecodemonth + datecodeday + datecodeyear;

Ideas? Is there anything in the format of the date that will do this?

dan

[Marc Gravell]

Um, any evidence of that?
I agree with Jon; the real demonstration here is when you have more
than 2 strings:

string d = a + b + c; // 3 existing strings

The point is, it /doesn't/ evaluate the left-to-right, which is what
you might reasonably expect, but which would create intermediate
strings (i.e. tmp = a+b, d = tmp + c). Instead the complier swaps it
for:

string d = string.Concat(a ,b,c);

Internally, string.Concat finds the sum of all the strings, allocates
a buffer big enough for all 3, and inserts the provided strings into
the buffer one after the other. Generally, you would have to use a
char[] buffer for this, but since the new string hasn't seen the
outside world yet, the runtime actually uses a string directly and
edits the (otherwise immutable) string directly.

Marc

[Marc Gravell]

is there expert opinion (yourselves included of course!) on when

to use String and when to use StringBuilder?

Jon's page is (as usual) quite illuminating:
http://www.pobox.com/~skeet/csharp/stringbuilder.html

Basically, if you are concatenating strings in a loop, then
StringBuilder is your friend. If you are concatenating strings in a
single line (i.e. someVar + "alkfj" + someOtherVar + whatever + "
items"), then just let the compiler do the work. You can also use
StringBuilder to retain editability of the contents while
concatenating, but I've never had to use this (I prefer to simply
build the correct string as I go)).
If you are writing an über-string (perhaps file contents, CSV
maybe...) then a third approach is to use a TextWriter to write
directly to an output Stream (such as a file, or an HttpResponse).
This can be even more efficient, as the working data is minimised -
very useful for server work or volume processing.

Marc