Pulling Digits Out of String to Sum Them

Problem/Question/Abstract:

How do I pull out every second digit from a string and sum them?

Answer:

This is a rather unusual question, but it's not that hard to accomplish.

What must iterate through each character of the string and "grab" the digits whose position is a multiple of two (2). There are a couple of ways to do this, but I took what I felt was the easier route. Since this is more or less a binary problem, setting a Boolean value with each iteration works nicely. Here's the logic:

For all "odd" positions, set Boolean value to False;
For all "even" positions, set Boolean value to True;
If the Boolean value is true, grab that character and add it to a temporary buffer.
Iterate through the buffer, and convert each character to an Integer while adding the converted value to an integer variable.

Here's the code that accomplishes the above:

function AddEvenOrOddChars(S: string; OddOrEven: Boolean): Integer;
var
  I: Integer;
  evn: Boolean;
  buf: string;
begin
  Result := 0;

  {If OddOrEven was passed as True, then the all odd positions
   will be grabbed and summed. If False, then all even positions
   will be grabbed and summed.}
  evn := EvenOdd;

  {First grab the even position characters}
  for I := 1 to Length(S) do
  begin
    if evn then
      buf := buf + S[I];

    {Set boolean to its opposite regardless of its current value.
     If it's currently true, then we've just grabbed a character.
     Setting it to False will make the program skip the next one.}
    evn := not evn;
  end;

  {Now, iterate through the buffer variable to add up the individual
   values}
  for I := 1 to Length(buf) do
    Result := Result + StrToInt(buf[I]);
end;