Question

I do apology in advance if there are many variables in the following code sample that their “types” is not clear to you, it is a big library, I just can’t put all of that in here, so think of it at high-level, and the name of the variables is kind of helpful too…

Problem: A “concept” can have many “relations”. Each of those relations can also have many concepts, For example like a father and child, a father has many children, a child may itsself be a father and has more children ,etc…
So I want to pass the root father and get all the hierarchy and write it to a file …

The high-level code I am using is this, THE PROBLEM IS THAT it Crashes by a Null exception when it gets the child that has no more children. So its object is null in this line:

oUCMRConceptReltn = moTargetConceptList.ConceptReltns.get_ItemByIndex(i, false);

So I thought well let’s put a not null check around it, yeah fixes the crash BUT after it sees the first leafe, it doesn’t go further and algorithm stops.
So Something is wrong with the way I am calling recursion, but can’t figure it out.

private void MyLoadMethod(string sConceptCKI)
{
    UCMRConceptLib.UCMRConceptLoadQual oUCMRConceptLoadQual = new UCMRConceptLib.UCMRConceptLoadQual();

    //Fill out UCMRConceptLoadQual object to get new list of related concepts
    moTargetConceptList.Load(oUCMRConceptLoadQual;

    // WHEN IT IS ZERO, THERE ARE NO MORE CHILDREN.
    int numberofKids = moTargetConceptList.ConceptReltns.Count();
    if (numberofKids == 0)
        return ;
    for (int i = 1; i <= numberofKids; i++)
    {
        oUCMRConceptReltn = moTargetConceptList.ConceptReltns.get_ItemByIndex(i, false);

            //Get the concept linked to the relation concept
            if (oUCMRConceptReltn.SourceCKI == sConceptCKI)
            {
                oConcept = moTargetConceptList.ItemByKeyConceptCKI(oUCMRConceptReltn.TargetCKI, false);
            }
            else
            {
                oConcept = moTargetConceptList.ItemByKeyConceptCKI(oUCMRConceptReltn.SourceCKI, false);
            }

            //write its name to the file...now recursion: go and find its children.
            builder.AppendLine("\t" + oConcept.PrimaryCTerm.SourceString);
            MyLoadMethod(oConcept.ConceptCKI);
    }
    return ;
}

Answer 1

Just as a side note, the check for number of kids being 0 is redundant, because you’re never going to enter the loop.

The algorithm looks okay for what you want to do. You don’t need to return anything in this case because your algorithm uses a side effect (the appendLine) to give your output.

I don’t know C#, but it looks to me as if you’re using some variables that are not local to the function, like oUCMRConceptReltn and oConcept. If they’re not local to the function, different recursive invocations can change those values in unexpected ways. Recursive functions should almost never write to a variable outside its own scope.