Finding Holes in Algorithms - "Number in String" (5979)

The 16 August quiz stated the following:

I need to write a function named plch_num_instr that returns the number of times a substring occurs within a string. Here is the header of the function:

FUNCTION plch_num_instr (
   string_in IN VARCHAR2, substring_in IN VARCHAR2)

We then asked you:

"Which of the choices implement plch_num_instr so that the following block displays these five lines after execution..."

One player wrote after taking this quiz:

"Fine quiz but I think that none of the solutions would correctly implement your requirement (although I found the three correct answers for the quiz). Just try "plch_num_instr( 'Steieimer Meieieier', 'eiei')". The correct answer is 3 but all of your solutions just return 2 (haven't tried it before, but I have thought that the RegExp_Count() should return the correct value). The error lies in the implementation of the answer with id 7628 where you add the length of the substring to the actual starting position instead of adding just 1. This is no request for a scoring adjustment just a little bit to think about."  He also offered a corrected implementation, which you will find at the end of this posting.

And another player wrote with a similar concern: "In the given function calls, it give us correct answers, but there are cases when this implementation returns incorrect answer. For example: plch_num_instr ('123123123123', '123123'). Call to this implementation will return 2, but substring '123123' occurs 3 times within a string."

And finally as one player so succinctly expressed it: "Just out of interest, given this specification what should the following block display? BEGIN DBMS_OUTPUT.put_line (plch_num_instr ('steeeeeeven', 'ee')); END;"

All players are correct; the choices did not contain an implementation that handled all cases (nor did we claim that they would). I will add the implementation you see below to the answer, along with the points noted above. But no change will be made in scoring.

CREATE OR REPLACE
FUNCTION InStrCount (pString  IN VARCHAR2,
                     pSearch  IN VARCHAR2)
                    RETURN BINARY_INTEGER
/*====================================================================
    Returns the number of occurrences of a search-string in a string
  --------------------------------------------------------------------
    pString:  String to search for the occurrences of "pSearch"
    pSearch:  String to search in "pString"
  --------------------------------------------------------------------
    Result:  number of occurrences of "pSearch" in "pString"
  --------------------------------------------------------------------
    History:  000-00  nhecker
  ====================================================================*/
IS

    Result  BINARY_INTEGER := 0;
    iPos    BINARY_INTEGER;
    iStart  BINARY_INTEGER := 1;

BEGIN
  LOOP
    iPos := InStr( pString, pSearch, iStart);
    EXIT WHEN (iPos = 0);

    Result := Result + 1;
    iStart := iPos + 1;
  END LOOP;
  RETURN (Result);
END InStrCount;
/