c-添加元素链表

Question

#include <stdio.h>
#include <stdlib.h>
typedef struct str_node {
int data;
struct str_node *next;
} node;
void create_list(node ** head, int n);
void display_list(node * head);
void add_e(node ** head);
int
main(void)
{
int n;
node *head;
head = NULL;
printf("Insert size of list: ");
scanf("%d",&n);
create_list(&head, n);
display_list(head);
add_e(&head);
display_list(head);
return 0;
}
void
display_list(node *head)
{
if (head == NULL) {
printf("Empty list.");
}
else {
while (head != NULL) {
printf("DATA: %dn", head->data);
head = head->next;
}
puts("null");
}
}


void create_list(node **head,int n){
node *new,*tmp;
int num,i;
*head = malloc(sizeof(node));
if(*head == NULL){
printf("Memory can not be allocated.");
}
else{
printf("Insert element 1: ");
scanf("%d",&num);
(*head)->data = num;
(*head)->next = NULL;
tmp = *head;
for(i=2;i<=n;i++){
new = malloc(sizeof(node));
if(new == NULL){
printf("Memory can not be allocated.");
break;
}
else{
printf("Insert element %d: ",i);
scanf("%d",&num);
new->data = num;
new->next = NULL;
tmp->next = new;
tmp = tmp->next;
}
}
}
}

void
add_e(node **head)
{
node *new;
int num;
new = malloc(sizeof(node));
if (new == NULL) {
printf("Memory can not be allocated.");
}
else {
printf("Insert element at the beginnig: ");
scanf("%d", &num);
new->data = num;
new->next = NULL;
while ((*head)->next != NULL) {
*head = (*head)->next;
}
(*head)->next = new;
}
}

我不明白为什么在使用add_e()函数后，display_list()函数只给我列表的最后两个数字。add_e()函数应该是在列表末尾添加一个元素。我做错了什么？

编辑：添加了create_list()函数，这样你可以更好地理解，但现在它告诉我要添加更多细节，所以我正在写一些东西。

Answer 1

在main中，n被单元化，因此您将得到随机/糟糕的结果。

add_e应该而不是在while中使用*head，甚至执行while。printf上写着"插入开头"，这是不同的/更简单的。这就是我目前编码/修复的内容。

如果您[真的]想插入/附加到列表的末尾，则需要使用循环。但是，循环仍然是不正确的，因为在找到结束时不想推进head。

我还修复了提示的printf和scanf

以下是代码的重构/修复版本，并注释了错误：

#include <stdio.h>
#include <stdlib.h>
typedef struct str_node {
int data;
struct str_node *next;
} node;
void create_list(node **head, int n);
void display_list(node *head);
void add_e(node ** head);
int
main(void)
{
int n;
node *head;
head = NULL;
// NOTE/BUG: n is unitialized
#if 1
n = 5;
#endif
create_list(&head, n);
display_list(head);
add_e(&head);
display_list(head);
return 0;
}
void
display_list(node *head)
{
if (head == NULL) {
printf("Empty list.");
}
else {
while (head != NULL) {
printf("DATA: %dn", head->data);
head = head->next;
}
puts("null");
}
}
void
create_list(node **head, int n)
{
node *new,
*tmp;
int num,
i;
*head = malloc(sizeof(node));
if (*head == NULL) {
printf("Memory can not be allocated.");
}
else {
printf("Insert element 1: ");
#if 1
fflush(stdout);
#endif
#if 0
scanf("%d", &num);
#else
scanf(" %d", &num);
#endif
(*head)->data = num;
(*head)->next = NULL;
tmp = *head;
for (i = 2; i <= n; i++) {
new = malloc(sizeof(node));
if (new == NULL) {
printf("Memory can not be allocated.");
break;
}
else {
printf("Insert element %d: ", i);
#if 1
fflush(stdout);
#endif
#if 0
scanf("%d", &num);
#else
scanf(" %d", &num);
#endif
new->data = num;
new->next = NULL;
tmp->next = new;
tmp = tmp->next;
}
}
}
}
void
add_e(node **head)
{
node *new;
int num;
new = malloc(sizeof(node));
if (new == NULL) {
printf("Memory can not be allocated.");
}
else {
printf("Insert element at the beginnig: ");
fflush(stdout);
scanf(" %d", &num);
new->data = num;
new->next = NULL;
#if 0
while ((*head)->next != NULL) {
*head = (*head)->next;
}
(*head)->next = new;
#else
if (*head == NULL)
*head = new;
else {
new->next = *head;
*head = new;
}
#endif
}
}

---

更新：

在add_e中，因为我不确定您是想在列表的开头[基于printf]还是在末尾[基于代码]插入，所以我创建了一个版本，该版本经过了更多的清理，并演示了这两种类型：

#include <stdio.h>
#include <stdlib.h>
typedef struct str_node {
int data;
struct str_node *next;
} node;
void create_list(node **head, int n);
void display_list(node *head);
void add_begin(node **head);
void add_end(node **head);
int
main(void)
{
int n;
node *head;
setbuf(stdout,NULL);
head = NULL;
printf("Enter initial number of list elements: ");
scanf(" %d",&n);
create_list(&head, n);
display_list(head);
add_begin(&head);
display_list(head);
add_end(&head);
display_list(head);
return 0;
}
void
display_list(node *head)
{
node *cur;
if (head == NULL) {
printf("Empty list.n");
}
for (cur = head;  cur != NULL;  cur = cur->next)
printf("DATA: %dn", cur->data);
}
void
create_list(node **head, int n)
{
node *new, *tmp;
int num, i;
tmp = *head;
for (i = 1; i <= n; i++) {
new = malloc(sizeof(node));
if (new == NULL) {
printf("Memory can not be allocated.");
break;
}
printf("Insert element %d: ", i);
scanf(" %d", &num);
new->data = num;
new->next = NULL;
if (*head == NULL)
*head = new;
else
tmp->next = new;
tmp = new;
}
}
// add_begin -- insert at before head of list
void
add_begin(node **head)
{
node *new;
int num;
new = malloc(sizeof(node));
if (new == NULL) {
printf("Memory can not be allocated.");
exit(1);
}
printf("Insert element at the beginning: ");
scanf(" %d", &num);
new->data = num;
new->next = *head;
*head = new;
}
// add_end -- add to tail/end of list
void
add_end(node **head)
{
node *new;
node *tmp;
node *tail;
int num;
new = malloc(sizeof(node));
if (new == NULL) {
printf("Memory can not be allocated.");
exit(1);
}
printf("Append element at the end: ");
scanf(" %d", &num);
new->data = num;
new->next = NULL;
// find the tail
tail = NULL;
for (tmp = *head;  tmp != NULL;  tmp = tmp->next)
tail = tmp;
if (tail != NULL)
tail->next = new;
else
*head = new;
}