Question

The following code is supposed to create a singly linked list in C. I wish to understand what insert_node does with pointer head. What does “head” points to each time insert_node is called?

struct node{
    int data;
    struct node* next; 
};
typedef struct node node;

    node* head = NULL; 

void insert_node(int data) {
    node *new_node = (node*) malloc(sizeof(node)); 
    new_node->data = data;
    new_node->next = head;
    head = new_node;
}

Answer 1

head will point to the beginning of the linked list (the first entry in the list). To get subsequent elements you just follow the next pointer inside the node.

Every time you add a new node, you set the next of the new element to the current head and set head to the new element so you chain the elements together.