不採用頭結點：

#include <stdio.h> // printf
#include <stdbool.h> // bool true false
#include <stdlib.h> // malloc EXIT_FAILURE EXIT_SUCCESS 

struct node {
    int value;
    struct node *next;
};

// 頭插法，時間複雜度O(1)
struct node *add_to_list(struct node *list, int n)
{
    struct node *new_node;
    
    new_node 
 
= malloc(sizeof(struct node));
    if (new_node == NULL) {
        printf("Error: malloc failed in add_to_list\n");
        exit(EXIT_FAILURE);
    }
    new_node->value = n;
    new_node->next = list;
    return new_node;
}

// 按值查詢表結點，時間複雜度O(n)
struct node *get_by_value(struct node *list, int n)
{
    
 
while (list != NULL && list->value != n) list = list->next;
    return list;
}

// 按序號查詢表結點，時間複雜度O(n)
struct node *get_by_position(struct node *list, int pos) 
{
    if (pos < 1) return NULL;
    
    int cur = 1;
    while (list != NULL && cur < pos) {
        list = list->next;
        cur
 
++;
    }
    return list;
}

void print_list(struct node *list) 
{
    printf("linked list: ");
    while (list != NULL) {
        printf("%d ", list->value);
        list = list->next;
    }
    printf("\n");
}


int main()
{
    struct node *first = NULL;
    
    first = add_to_list(first, 10);
    
    first = add_to_list(first, 20);
    
    first = add_to_list(first, 30);
    
    first = add_to_list(first, 40);
    
    print_list(first); // => 40 30 20 10
    
    printf("%d\n", get_by_value(first, 10)->value); // => 10
    
    printf("%d\n", get_by_position(first, 3)->value); // => 20
    

    // 刪除第3個結點
    struct node *p = get_by_position(first, 3 - 1);
    p->next = (p->next)->next;
    
    print_list(first); // => 40 30 10
    
    // 刪除第1個結點
    first = first->next;
    
    print_list(first); // => 30 10
    
    // 無頭結點的單鏈表，操作第1個結點往往需要“特殊處理”。 
    
    return 0;
}

引入頭節點的好處是：便於處理首個數據元素。