Question

I’m not very advanced in the sorting part of programming yet, so I was looking for some help with my algorithm.

void sortList()
{
    Item_PTR tmpNxt = current->nextItem;
    Item_PTR tmpPTR = current;
    int a, tmp;

    while(tmpNxt != NULL)
    {   
        a = tmpPTR->value;
        while(tmpNxt != tmpPTR && tmpNxt->value < a)
        {
            tmp = a;
            tmpPTR->value = tmpNxt->value;
            tmpNxt->value = tmp;
            tmpPTR = tmpPTR->nextItem;
        }
        tmpPTR = current;   
        tmpNxt = tmpNxt->nextItem;
    }

}

The list state before sorting: 9 8 7 6 5 4 3 2 1
after sorting: 1 9 8 7 6 5 4 3 2

I’m not sure why…I’ve played computer a lot on paper and I feel like it should work…but maybe other eyes will spot the problem.

Current is a global pointer that will always have the location of the first/ top element in the list.

Answer 1

This is because the function sortList() is not changing current, the “global”
variable denoting the list head.

Please don’t use a global variable, and certainly not for a linked list head. (What will you do when you need two lists?)

I would redesign the sortList() function to either one of the following:

/* sort the list pointed to by phead and return the new head after sorting */
Item_PTR sortList( Item_PTR phead );

/* sort the list pointed to by *pphead */
void sortList( Item_PTR * pphead );

Also, make yourself familiar (even if you can’t use them in the immediate project) to the interface of C++ Standard Library for lists, std::list link