我应该在此代码中进行哪些更改以使其打印某些内容？ 插入 function 是否需要是 struct 类型才能插入节点？

Question

I honestly don't really understand how this code works. To make it work would I just need to change the type of some of the functions or would I need to change more than that?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct LinkedList{
    int data;
    struct LinkedList* next;
};
int main(){
    struct LinkedList *A = NULL;
    insert(A, 3);
    printList(A);
    return 0;
}
void insert(struct LinkedList *root, int item){
   root=malloc(sizeof(struct LinkedList));
   root->data= item;
   root->next = NULL;
}
void printList(struct LinkedList *head){
    struct LinkedList *temp=head;
    while (temp != NULL){
        printf("%d", temp->data);
        temp = temp->next;
    }
}

Answer 1

It is necessary to pass as a parameter to "insert" function a pointer to the "struct LinkedList" pointer... not the "struct LinkedList" pointer itself.

Additionally, you are only calling "insert()" once in this version so you don't see and your "insert()" is not creating the linked list. Instead it is overwriting the "head" (your "A" pointer) every time it is called.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct LinkedList{
    int data;
    struct LinkedList* next;
};
/* prototypes */
void insert(struct LinkedList **root, int item);
void printList(struct LinkedList *head);

int main(){
    struct LinkedList *A = NULL;
    insert(&A, 3);
    insert(&A, 4);
    printList(A);
    return 0;
}
void insert(struct LinkedList **root, int item){

   struct LinkedList *newptr;

   newptr=malloc(sizeof(struct LinkedList));
   newptr->data= item;
   // ORIGINAL: root->next = NULL;
   newptr->next = *root;

   *root = newptr;
}
void printList(struct LinkedList *head){
    struct LinkedList *temp=head;
    while (temp != NULL){
        printf("%d\n", temp->data);
        temp = temp->next;
    }
}