Pointers being declared in structs in c

Question

    struct charact
{
    char ch;
    int occurs;
    struct charact *next;
};

What is "next" in this struct exactly?

Answer 1

What is "next" in this struct exactly?

next is a struct charact pointer. It can be used to point at instances of struct charact or NULL to indicate that it's not pointing at a struct charact.

This particular struct looks like it is a node in a forward linked list. That is, a linked list that only has references to the next element in the list.

A (double) linked list would also have a struct charact pointer to be able to point at the previous element in the list:

struct charact
{
    char ch;
    int occurs;
    struct charact *prev;
    struct charact *next;
};

For such a node, linking them together could look like this:

struct charact a = {.ch = 'a'};
struct charact b = {.ch = 'b'};
struct charact c = {.ch = 'c'};
a.next = &b;
b.prev = &a;
b.next = &c;
c.prev = &b;

struct charact *head = &a;
struct charact *tail = &c;

Here head would point at a. a.next points at b and b.next points at c - and you would have the ability to go backwards in such a list too via the prev member:

// backwards:
for(struct charact *curr = tail; curr != NULL; curr = curr->prev) {
    printf("%c\n", curr->ch);
}

// forward:
for(struct charact *curr = head; curr != NULL; curr = curr->next) {
    printf("%c\n", curr->ch);
}

Note: The actual instances of list nodes are usually not created as automatic variables like above but created and destroyed dynamically using malloc/free.