C difference between (!pointer) and (pointer != NULL),

Question

I'm currently learning how to code C and stumbled upon an interesting line,

Apparently,

struct node{
    node *next;
};

node *head = (node *)calloc(1, sizeOf(node));
head->next = NULL;

node *currentNode = head;
while (!currentNode)

In this context, is

while(!currentNode)

different to

while(currentNode != NULL)

? I thought they meant to check for the same stuff, when current Node is not NULL but they are returning different results and I dont' understand...

Answer 1

while(currentNode)

and

while(currentNode != NULL)

are equivalent.

The first says that while currentNode has some value (could be anything, even garbage), the second one says that while currentNode is not NULL , ie, has some value.

On the other hand,

while(!currentNode)

means that while currentNode does not hold any value, ie, is NULL .