Update readmes

30_Cube/README.md

@@ -16,3 +16,27 @@ http://www.vintage-basic.net/games.html
 #### Porting Notes
 
 (please note any difficulties or challenges in porting here)
+
+##### Randomization Logic
+
+The BASIC code uses an interesting technique for choosing the random coordinates for the mines. The first coordinate is
+chosen like this:
+
+```basic
+380 LET A=INT(3*(RND(X)))
+390 IF A<>0 THEN 410
+400 LET A=3
+```
+
+where line 410 is the start of a similar block of code for the next coordinate. The behaviour of `RND(X)` depends on the
+value of `X`. If `X` is greater than zero then it returns a random value between 0 and 1. If `X` is zero it returns the
+last random value generated, or 0 if no value has yet been generated.
+
+If `X` is 1, therefore, the first line above set `A` to 0, 1, or 2. The next 2 lines replace a 0 with a 3. The
+replacement values varies for the different coordinates with the result that the random selection is biased towards a
+specific set of points. If `X` is 0, the `RND` calls all return 0, so the coordinates are the known. It appears that
+this technique was probably used to allow testing the game with a well-known set of locations for the mines. However, in
+the code as it comes to us, the value of `X` is never set and is thus 0, so the mine locations are never randomized.
+
+The C# port implements the biased randomized mine locations, as seems to be the original intent, but includes a
+command-line switch to enable the deterministic execution as well.

30_Cube/csharp/README.md

@@ -1,3 +1,12 @@
 Original source downloaded [from Vintage Basic](http://www.vintage-basic.net/games.html)
 
 Conversion to [Microsoft C#](https://docs.microsoft.com/en-us/dotnet/csharp/)
+
+#### Execution
+
+As noted in the main Readme file, the randomization code in the BASIC program has a switch (the variable `X`) that
+allows the game to be run in a deterministic (non-random) mode.
+
+Running the C# port without command-line parameters will play the game with random mine locations.
+
+Running the port with a `-d` command-line switch will run the game with non-random mine locations.