C 链表节点不添加

Question

我想在头节点或其他节点后面添加新节点，但节点不添加 whay 我应该怎么做吗？

#include <stdio.h>
#include <stdlib.h>
typedef struct node {
int val;
struct node *next;
} Node;
Node *head, *tail, *behind, *prev,*twonext;
Node *new_node(int val){
struct node *ptr = malloc(sizeof(*ptr));
if(ptr==NULL){
    perror("malloc:");
    printf("nFailed to create a new node.n");
    return NULL;
}
ptr->val  = val;
ptr->next = NULL;
return ptr;
}
Node *creatFirstNode(int val){
return head = tail = new_node(val);
}
void printList(void){
Node *np = head;
printf("n----Value in Liked list----n");
while(np){
    printf("[%d], ", np->val);
    np = np->next;
}
 // printf("NULLn");
}
void freeList(void){
while(head){
    Node *np = head->next;
    free(head);
    head = np;
}
tail = NULL;
}
int main(void){
char cmd =' ';
int k;
printf("n-------- Welcome to Linked List Program -----------nn");
do {
    int v = 0;
    int s = 0;
    printf("nAdd to 'h'ead or 't'ail or 'b'ehind value or 'p'rint or 'q'uit:");   
    scanf(" %c", &cmd);
    fflush(stdin);
    switch(cmd){

添加头节点--------------------------------------------------------------------

    case 'h':
        printf("Enter value node head:");
        scanf("%d", &v);
        if(head == NULL){
            creatFirstNode(v);
        } else {
            Node *np = new_node(v);
            np->next = head;
            head = np;
        }
        fflush(stdin);
        printList();
        break;

添加尾节点--------------------------------------------------------------------

    case 't':
        printf("Enter value node tail:");
        scanf("%d", &v);
        if(head == NULL){
            creatFirstNode(v);
        } else {
            tail = tail->next = new_node(v);
        }
        fflush(stdin);
        printList();
        break;

添加到节点后面，我在这里有问题怎么办?? -----------------------------------------------

    case 'b':
            printf("Enter node value:");
            scanf("%d",&v);
            Node *np = new_node(v);
            printf("Adding value [%d] in new node:",v);
        //  behind = behind->next = new_node(v);
        if(head == NULL)
        {
        printf("No node to insert behind:");
        }
        else
        {
            printf("nAdd new node behind the value:");
            scanf("%d", &s);
            np = head;
            while(np->val != s);
            {
                prev=np;
                np =np->next;
            }
            twonext=np->next;
            np->next=NULL;
            np->next=twonext;
        }
        fflush(stdin);
        printList();
        break;

---

    /*case 'p':
        printList();
        break;
        */
    case 'q':
        freeList();
        printf("nBye!n");
        getch();
        break;
    default:
        printf("n     Invalid Input     ");
    }
}while(cmd != 'q' );
return 0;
}

Answer 1

基本上，

如果你想在其他节点之间放置一个新节点，你必须将上一个节点链接到下一个节点>下一个节点，将新节点>下一个节点链接起来。仅此而已，下面是一个代码示例。

case 'b':
            printf("Enter node value:");
            scanf("%d",&v);
            Node *np = new_node(v);
            printf("Adding value [%d] in new node:",v);
        //  behind = behind->next = new_node(v);
        if(head == NULL)
        {
            printf("No node to insert behind:");
        }
        else
        {
            printf("nAdd new node behind the value:");
            scanf("%d", &s);
            Node *tmp = head; /*You need a tmp variable to go through the list*/
            while(tmp->val != s && tmp != NULL);
            {
                prev=tmp; /*Save the prev node*/
                tmp =tmp->next; /*Go through*/
            }
            if(tmp != NULL){
                prev->next = np; /*Link the prev with the new*/
                np->next = tmp; /*Link the new one with the subsequent*/
            }
        }
        fflush(stdin);
        printList();
        break;