Roy Osherove’s string calculator kata has been implemented in a number of languages, after trying it a couple of days ago and liking it I created a screen cast of my attempt. Incidentally if you want to view it is maybe best to view in high definition on vimeo.

I have added a download which includes the build script, two source files and the Xcode language specification file, more details of where to place the specification file is available on developer.apple. Something I noticed about watching the screen cast back is Xcode’s code completion for SC++L is really poor, IIRC the only suggestion in the whole the kata is for stringstream’s method “tellg”. It would be interesting to see how much more productive I am using an IDE I have used for years such as Visual Studio.

Finally if anybody has any comments either positive or negative then please do feel free.

1. Create a simple String calculator with a method int Add(string numbers)
   1. The method can take 0, 1 or 2 numbers, and will return their sum (for an empty string it will return 0)
      for example “” or “1” or “1,2”
   2. Start with the simplest test case of an empty string and move to 1 and two numbers
   3. Remember to solve things as simply as possible so that you force yourself to write tests you did not think about
   4. Remember to refactor after each passing test
2. Allow the Add method to handle an unknown amount of numbers
3. Allow the Add method to handle new lines between numbers (instead of commas).
   1. the following input is ok:  “1\n2,3”  (will equal 6)
   2. the following input is NOT ok:  “1,\n”
   3. Make sure you only test for correct inputs. there is no need to test for invalid inputs for these katas
4. Allow the Add method to handle a different delimiter:
   1. to change a delimiter, the beginning of the string will contain a separate line that looks like this:
      “//[delimiter]\n[numbers…]” for example “//;\n1;2” should return three where the default delimiter is ‘;’
   2. the first line is optional. all existing scenarios should still be supported
5. Calling Add with a negative number will throw an exception “negatives not allowed” - and the negative that was passed.