Notes on Pointers and LinkedList in C

Three important things to know about pointers in C

1. What is pointer in C

A pointer is a variable that stores the address of another variable.

2. Two ways to access a pointer

Direct Access by variable name;
Indirect Access by address.

3. Mind the Memory Locate (IMPORTANT)

Unlike
int a[10]; which allocated 10 * 4 bytes in memory,
int *p; only allocated 8 bytes in memory to store the address of another variable.

A pointer that’s not been initialized is called a “wild pointer”, which address stored is a random one;
A pointer point to 0x0 or NULL is a “null pointer”.

Do NOT access a wild pointer or a null pointer. This will cause  Segmentation fault (core dumped)  error.

Pointers and Struct

When using pointer to point to a struct, it must ne initialized. i.e.

struct *Foo f = (struct Foo*)malloc(sizeof(struct Foo));

And to access members in the struct, -> must be used instead of . i.e.

struct Foo f1;
struct *Foo f2 = (struct Foo*)malloc(sizeof(struct Foo));

int a = f1.num;
int b = f2->num;

LinkedList Using Struct Pointers

Initialize Nodes Using for Loop

// initialize head
struct Node *head = (Node *)malloc(sizeof(Node));
head->data = 0;
head->next = NULL;

// set tail to head
struct Node *tail = head;

// initalize the rest of nodes
for (int i = 0; i < size - 1; i++)
{
    // initalize a new node
    struct Node *newNode = (Node *)malloc(sizeof(Node));
    newNode->data = 0;
    
    // set newNode to be the next node and tail of the list
    tail->next = newNode;
    tail = tail->next;
    
    // set the tail's next to NULL
    tail->next = NULL;
}