打印链表时出现意外输出

Question

我在 lubuntu 16.04 的代码块 13.12 上得到了这段代码

程序是运行但是问题是第一次插入是重复的也就是

假设我首先将整数“4”插入链表。但我得到的输出为：

4 ,4 ,

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

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

struct node* head = NULL;

void Insert(int c)
{
if(head == NULL) {
    struct node* temp = malloc(sizeof(struct node));
    temp -> data = c;
    temp -> next = NULL;
    head = temp;
}

struct node* temp = malloc(sizeof(struct node));
temp -> data = c;
temp -> next = NULL;
struct node* temp1 = head;

    while (temp1->next != NULL) {
        temp1 = temp1->next;

}
temp1 -> next = temp;
    }


void print() {

    struct node* temp = head;
    printf("list is: \n");
    while (temp != NULL) {

        printf( "%d ,",temp->data);
        temp = temp->next;
    }
}


int main () {

printf("How Many Numbers?\n");
int a ,b ,c;
scanf("%d" , &b);
for(a = 0;a<b;a++) {
    printf("Enter the numbers \n");
    scanf("%d",&c);
    Insert(c);
    print();
}
return 0;
}

Answer 1

那是因为Insert函数"falls through"在初始化第一项后，再次插入。在代码块末尾添加return。

void Insert(int c)
{
if(head == NULL) {
    struct node* temp = malloc(sizeof(struct node));
    temp -> data = c;
    temp -> next = NULL;
    head = temp;
    return;        //<-- add this line
}
...

Answer 2

the problem is that the first insertion is duplicated

原因：

你已经正确地提到了if(head==NULL)来检查插入的节点是否是第一个节点但是之后你没有提到else 限制编译器。
所以编译器编译了 if 块和它后面的代码
因此在 head 之后创建了另一个具有相同值 c
这就是当您插入 c=4 时，您得到 4,4, 作为输出的原因

解决方案

尝试将您的 insert() 与 else 条件一起使用

void Insert(int c)
{
    if(head == NULL)
    {
        struct node* temp = malloc(sizeof(struct node));
        temp -> data = c;
        temp -> next = NULL;
        head = temp;
    }
    else
    {
        struct node* temp = malloc(sizeof(struct node));
        temp -> data = c;
        temp -> next = NULL;
        struct node* temp1 = head;
        while (temp1->next!= NULL)
            temp1 = temp1->next;
        temp1 -> next = temp;
     }
}

建议 : 你在insert()函数中提到过两次

    struct node* temp = malloc(sizeof(struct node));
    temp -> data = c;
    temp -> next = NULL;

只需分配一次temp，然后使用if-else条件将其插入到适当的位置。这也减少了代码行数。这样做：

void Insert(int c)
{
    struct node* temp = malloc(sizeof(struct node));
    temp -> data = c;
    temp -> next = NULL;

    if(head == NULL)
    {
        head = temp;
    }
    else
    {
        struct node* temp1 = head;
        while (temp1->next!= NULL)
            temp1 = temp1->next;
        temp1 -> next = temp;
    }
}

打印链表时出现意外输出

Unexpected output while printing a linked list

c

ubuntu

linked-list

codeblocks

data-structures