Simplify Do While Loop Checking for Null Pointer - c++

Question

I have a really basic problem that I can't figure out. I'm using chaining with hash tables to store nodes that collide with each other. I used a do while loop to print the first node at least once, and continue to print the chained nodes if they exist. However, in order to traverse the chained list, I need to change the address of the node for the next loop. Any way I try writing this, I find myself repeating code, which I was trying to avoid by using this loop. Please help
do {
cout << "Bid id: " << table.at(i)->bidId << " title: " << table.at(i)->title <<
" fund: " << table.at(i)->fund << " amount: " << table.at(i)->amount << endl;
if (table.at(i)->next!=nullptr){//check if first node has next node
table.at(i) = table.at(i)->next; //change address to the next pointer
}// how do I avoid repeating my condition below?
}
while (table.at(i)->next!=nullptr);

Answer 1

This code will replicate the functionality in your loop without duplicating the check against NULL.
while(true)
{
cout << /* stuff */ endl;
auto next = table.at(i)->next;
if(next)
table.at(i) = next;
else
break;
}
From the description though, are you sure you want to reassign the values inside your hash map while looping over them? I suspect that this code may suit your intent/needs better:
auto current = table.at(i);
while(current)
{
cout << /* stuff */ endl;
current = current->next;
}

Answer 2

When you find yourself in a situation like this one, it's a good idea to question your premise. In this case, I am talking about your assumption that you need a do while loop.
If there is a chance that your data won't be there or that your container is empty, then a do while won't do the job because it will loop at least once.
Generally, for iterating through a collection of data you'll want to use a for or while loop.

Answer 3

If I understand the code correctly, you need a precondition loop and not a postcondition one, as you have right now. For example:
while (table.at(i)) {
cout << "Bunch of stuff";
table.at(i) = table.at(i)->next;
}

Answer 4

You could try doing:
for(auto node = table.at(i)->next;node!=nullptr;node=node->next)
cout << "Bid id: " << node->bidId << " title: " << node->title;
Where you may need to replace node = table.at(i)->next with an appropriate way of getting a link to the first entry.

Answer 5

You can use C++11's range based for loop here. All you want to know is that value->next is not a nullptr before doing the assignment. Rest all is taken care by the simple and modern range based for loop
for(auto const& value: table) {
if (value->next != nullptr) {
value = value->next;
}
}
Its even faster and safer this way

Answer 6

If really you want to be able to get last element after the loop, you may do:
do {
cout << "Bid id: " << table.at(i)->bidId
<< " title: " << table.at(i)->title
<< " fund: " << table.at(i)->fund
<< " amount: " << table.at(i)->amount << endl;
if (table.at(i)->next == nullptr){
break;
}
table.at(i) = table.at(i)->next;
} while (true);
// table.at(i) != nullptr && table.at(i)->next == nullptr