Question

I wrote a couple functions for a school project, and I have them working but I don’t understand why. they should be identical but they only work if one checks current->link and the other checks current itself. Shouldn’t both loops be current != NULL?

The two functions are called in main like so:

customerHead = fillCart(limit, lowLevelInv); //fills linked list
totCart(customerHead, lowLevelInv);                 
printCart(customerHead, lowLevelInv);

This one only works if the while loop checks current != NULL

int totCart(OrderPtr head, inventory lowLevelInv[])
{
OrderPtr current;
current = head;
int tot = 0;

while(current != NULL)
{
    tot += lowLevelInv[current->itemID].cost*current->qtyReceived;
    current = current->link;
}
cout<<"Cart total is: "<<tot<<endl;
return tot;
}

This one only works if the while loop checks current->link !=NULL

void printCart(OrderPtr head, inventory lowLevelInv[])
{
OrderPtr current;
current = head;

cout<<"you have ordered: \n";

while(current->link != NULL);
{
    cout<<current->orderID<<": "<<current->qtyReceived<<" "    <<lowLevelInv[current->itemID].name<<" for "<<lowLevelInv[current->itemID].cost*current->qtyReceived<<endl;
    current = current->link;
} 
}

Answer 1

Looks like the problem is here:

while(current->link != NULL);
{
    cout<<current->orderID<<": "<<current->qtyReceived<<" "    <<lowLevelInv[current->itemID].name<<" for "<<lowLevelInv[current->itemID].cost*current->qtyReceived<<endl;
    current = current->link;
} 

If you look very carefully, you have a spurious semicolon after the controlling statement in the “while” statement. That means that your program will hang if current->link is ever not null, since nothing ever changes current or current->link.

If that’s not actually your problem (because of a copy pasta problem, for example) you should show us how you’re building your list and what you specifically mean by “doesn’t work”.