做，而在我的基本单链表实现好笑C.请找出错误

Question

实现很好。没有编译错误，一切正常。只是do-while结构似乎在不应该重复的时候重复了两次。例如，如果为"插入新节点"选择"i"，则case应该切换到"i"，调用insert函数，然后遍历列表。它确实会这样做，但也会再次打印do-while循环中的所有内容，并打印默认情况。

我将在我的代码输出后发布代码。

下面是我的C代码，它实现了一个链表，以及它的基本遍历和插入函数:

#include <stdio.h>
#include <stdlib.h>
struct node
{
    int data;
    struct node *next;
};
void traverse(struct node *);
void insert(struct node **);
int main()
{
    char choice;
    struct node *head,**tohead;
    head=(struct node *)malloc (sizeof(struct node));
    tohead=&head;
    //STACKOVERFLOW NOTE: this is where I think the relevant portion begins
    do
    {
        printf("nChoose operation to perform:n");
        printf("tInsert a node(i)n");
        printf("tShow currenct linked list(s)n");
        printf("tQuit without saving changes(q):t");
        scanf("%c",&choice);
        switch(choice)
        {
            case 'i':
                insert(tohead);
                break;
            case 's':
                traverse(head);
                break;
            case 'q':
                printf("QUITTINGn");
                break;
            default:
                printf("Invalid choicen");
        }
    }while(choice!='q');
}//STACKOVERFLOW NOTE: This is where I think relevant portion ends. Possibly.
void traverse(struct node *p)
{
    printf("Linked list looks like: ");
    if(p->next==0)
    {
        printf("nothing. It's EMPTY");
        p->next==NULL;
    }
    else
    {   while(p->next!=NULL)
        {
            printf("%dt",p->data);
            p=p->next;
        }
        printf("%d",p->data);
    }
    printf("n");
}
void insert(struct node **pp)
{
    int value,position;
    struct node *q;
    q=*pp;
    struct node *newnode=(struct node *)malloc(sizeof(struct node));
    printf("Insert what number?:t");
    scanf("%d",&value);
    printf("In what position? Push '0' for last,'1' for first");
    printf("nttORnenter position no.:t");
    scanf("%d",&position);
    newnode->data=value;
    if(position==1)
    {   newnode->next=q;
        *pp=newnode;
    }
    else if(position==0)
    {
        while(q->next!=NULL)
            q=q->next;
        q->next=newnode;
        newnode->next=NULL;
    }
    else if(position>1)
    {
        int i;
        for(i=1;i<position-1;i++)
            q=q->next;
        newnode->next=q->next;
        q->next=newnode;
    }
    else
        printf("Invalid Position");
    traverse(*pp);
}

注意do-while语句是如何重复的，并且说'Invalid choice'

user@host: ~ $ ./a.o ut

Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): i
Insert what number?:    5
In what position? Push '0' for last,'1' for first
        OR
enter position no.: 0
Linked list looks like: 0   5
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): Invalid choice
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): i
Insert what number?:    3
In what position? Push '0' for last,'1' for first
        OR
enter position no.: 1
Linked list looks like: 3   0   5
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): Invalid choice
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): i
Insert what number?:    2
In what position? Push '0' for last,'1' for first
        OR
enter position no.: 3
Linked list looks like: 3   0   2   5
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): Invalid choice
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): s
Linked list looks like: 3   0   2   5
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): Invalid choice
Choose operation to perform:
    Insert a node(i)
    Show currenct linked list(s)
    Quit without saving changes(q): q
QUITTING
user@host:~$ 

Answer 1

当您使用Scanf输入任何内容时，您将以换行符结束。问题是scanf函数只提取请求的输入，而将换行符留在输入缓冲区中，因此在下一次迭代中，程序读取并提取该换行符，并将其视为无效输入并再次循环。

这很容易解决:在"%c"格式代码之前添加额外的空间，所以它是

scanf(" %c",&choice);
/*     ^           */
/*     |           */
/* Note space here */

这将告诉scanf读取和丢弃所有前导空格(换行符是)。

我还建议您阅读例如scanf参考。