Question

For some reason my function to delete a node from the middle of a list is deleting the first node instead of the one specified by the user. Here’s my function:

template< class NODETYPE >
bool List< NODETYPE >::removeMiddle( NODETYPE &value, int i )
{
    ListNode <NODETYPE> * tempPtr = firstPtr;
    int counter=1;

    if ( isEmpty() )
        return false;
    if (i <= 0)
        return false;

    while (tempPtr != 0 && counter < i){
        counter++;
        if ( firstPtr == lastPtr )
            firstPtr = lastPtr = 0;
        else
            firstPtr = firstPtr->nextPtr;

        if (counter == i){
            value = tempPtr->data;  // data being removed
            delete tempPtr;
        }

    }

    return true;
    RecordCounter--;
}

Can anyone help point me in the right direction?

Answer 1

I’m assuming it’s because this:

 if ( firstPtr == lastPtr )
     firstPtr = lastPtr = 0;
 else
     firstPtr = firstPtr->nextPtr;

should check and modify tempPtr, not firstPtr.

Since you don’t check by tempPtr, your function calls

if (counter == i){
   value = tempPtr->data;  // data being removed
   delete tempPtr;
}

but tempPtr was initially set to firstPtr and never modified afterwards.

Of course, you could have easily spotted this by debugging a bit, so I won’t correct the code for you, but this is a good starting point.