Question

Here is a part of code for deleting an element from the tail a singly Linked List:

int SLList::deleteFromTail()
{
    int el = tail->info;

    //if the list has only one element
    if(head == tail) {
        delete head;
        head = tail = 0;
    }
    else {
        //some code here...
    }

    return el
}

Here head and tail are pointers to first and last element of LL, respectively.

In the if block above after delete head we are setting head = tail = 0.

But after we have deleted head, how can we set it’s value to something? (NULL in this case)

Answer 1

Head is a pointer. You are deleting an object pointed by the pointer, not the pointer itself

Consider this example:

Foo *foo = new Foo(); //foo does not store Foo object. Just an adress of created object.
//do some stuff
delete foo; //object is deleted
foo = new Foo(); //create another Foo and make foo point to it

EDIT
A pointer is just an adress ob an object. When you write delete head you delete the object pointed by head, but even after deletion head pointer will point to the same place as before. But dereferencing it (e.g. *head) will cause problems.