有人可以帮我调试链表上的这段代码吗

Question

So, I tried to write a code for handling all basic operations of linked list. But some functions are not working properly and are exiting the code without showing any error. I have tried to do create, display, search, insert at end, insert at index, delete at data, delete at node. //create #include <stdio.h> #include <stdlib.h>

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

void Display(struct node *header)
{
    struct node *p;
    p = header;
    int i = 1;
    while (p->next != NULL)
    {
        printf("Data in Node %d is: %d\n", i++, p->data);
        p = p->next;
    }
}

void search(struct node *ptr, int q,int p)
{
    int i = 1;
    while (ptr->data != q)
    {
        ptr = ptr->next;
        i++;
        if(i==p)
        {
            printf("Invalid");
            break;
        }
    }
    printf("Node %d is %d\n", i, ptr->data);
}

struct node *insert_end(struct node *head, int p,int q)  //error
{
    int i=1;
    struct node *last;
    last->next = NULL;
    last->data = p;
    while(i<q)
    {
        head=head->next;
    }
    head->next = last;
    return last;
    
}

void insert_index(struct node *head, int p,int q, int a)  //error
{
    int i=1;
    struct node *new = (struct node *)malloc(sizeof(struct node));
    if(q>a)
    printf("Invalid");
    else{
    while(i<q-1)
    {
        head=head->next;
        i++;
        printf("!");
    }
    new->data=p;
    new->next=head->next;
    head->next=new;}
    
}

void delete_data(struct node *head,int x)  //error
{
    struct node *ty;
    while(head->data!=x)
    {
        head=head->next;
    }
    ty=head->next;
    head->next=ty->next;
    
}

void delete_node (struct node *head, int index)
{
    int i = 1;
    while (i <= index - 2)
    {
        head = head->next;
        i++;
    }
    struct node *ptr = head->next;
    head->next = ptr->next;
    free(ptr);
}

    int main()
{
    int n,t=1;
    struct node *ptr=(struct node *)malloc(sizeof(struct node));
    struct node *new1 = (struct node *)malloc(sizeof(struct node));
    struct node *start=ptr;
    printf("Enter Data[Input -1 to stop]:");
    while(n!=-1)
    {        
        scanf("%d",&n);
        ptr->data=n;
        if(n!=-1)
        ptr=ptr->next;
        t++;
    }
    ptr->next=NULL;
    int z,r,s;
    pq:
    printf("Enter 1 to Display Elements:\n");
    printf("Enter 2 to Search for a Data:\n");
    printf("Enter 3 to Insert Data at the End:\n");
    printf("Enter 4 to Insert Data at any Index:\n");
    printf("Enter 5 to Delete a data:\n");
    printf("Enter 6 to Delete a node:\n");
    printf("Enter -1 to Exit:");
    scanf("%d",&z);

    switch(z)
    {
        case 1: Display(start); break;  //display
        case 2:
            Display(start);
            printf("Enter data to Search:"); // search for a data
            scanf("%d", &r);
            search(start, r,t);
            goto pq;
        case 3:
            Display(start);
            printf("Enter data:"); // insert at end
            scanf("%d", &r);
            new1=insert_end(start, r,t);
            Display(start);
            goto pq;
        case 4:
            Display(start);
            printf("Enter data:"); // insert with index
            scanf("%d", &r);
            printf("Enter Index:");
            scanf("%d", &s);
            insert_index(start, r, s, t);
            Display(start);
            goto pq;
        case 5:
            Display(start);  //deleting with given data
            printf("Enter data to delete:");
            scanf("%d",&r);
            delete_data(start,r);
            Display(start);
            goto pq;
        case 6: Display(start);  //deleting a node
            printf("Enter Index:");
            scanf("%d", &s);
            delete_node (start, s);
            Display(start);
            goto pq;
        case -1: printf("Exiting");
        default:printf("Invalid");
                break;
    }
        
    return 0;
}

Functions insert_end, insert_index and delete_data are not working.

Answer 1

insert_end function does not malloc for last:

struct node *insert_end(struct node *head, int p,int q)  //error
{
    int i=1;
    struct node *last;
    last->next = NULL;
    last->data = p;

Answer 2

on insert_index you are setting the new node to set it's next field to the head node, and then also telling the head node to set it's next field to the new node. effectively pointing to each other.

On delete, you are changing the literal value of the head pointer. See below for another way. index will work the same as insert_end if you specify an index thats larger than the total size.

void insert_index(struct node *head, int data, int index)
{
    int i = 1;
    struct node *new = (struct node *)malloc(sizeof(struct node));
    struct node *temp = head;
    while(temp->next)
    {
        if (i == index)
        {
            break;
        }
        i++;
        temp = temp->next;
    }
    new->data = p;
    new->next = NULL;
    if (i == index)
    {
        new->next = temp->next->next;
    }
    temp->next=new;
}

void delete_data(struct node *head, int value)
{
    struct node *temp = head;
    while(temp)
    {
        if(temp->data == value)
        {
            temp->data = 0;
        }
        temp=temp->next;
    }
    
}

Answer 3

Before inserting a node, you need to initialize the node, including allocating memory for the node pointer and initializing the members of the node.

struct node *insert_end(struct node *head, int p,int q)
{
    int i=1;
    struct node *last;
    last = malloc (sizeof(struct node));
    last->next = NULL;
    last->data = p;
}

The p and q parameters of insert_index are not initialized, and you need to explicitly locate the insertion position according to q. The function delete_data needs to determine whether the head is NULL before comparing the data, and the node memory needs to be released after deleting the node.

Answer 4

Users in the answers have already pointed out some errors and the ways to fix them. But I'm afraid that the author still has much more to fix. To find out the reasons why the program doesn't work, I ran the static code analyzer against your code.

struct node *insert_end(struct node *head, int p,int q)  //error
{
    int i=1;
    struct node *last;
    last->next = NULL;
    last->data = p;
    while(i<q)
    {
        head=head->next;
    }

Warning: V776 Potentially infinite loop. The variable in the loop exit condition 'i < q' does not change its value between iterations.

The i variable is not changed in the loop, so the loop is executed until the list runs out and the null pointer is dereferenced.

int main()
{
    int n,t=1;
    struct node *ptr=(struct node *)malloc(sizeof(struct node));
    struct node *new1 = (struct node *)malloc(sizeof(struct node));
    struct node *start=ptr;
    printf("Enter Data[Input -1 to stop]:");
    while(n!=-1)

Warning: V614 Uninitialized variable 'n' used.

The n variable is not initialized by anything. The use of uninitialized variables leads to undefined behavior . Practically, this means that the variable can be equal to anything and we can't predict whether the loop will execute or not.

Static code analysis may be a great tool for code studying. The analyzer certainly can't replace human assistance, but it also can point out quite many errors. And you can immediately detect errors rather than waiting for an answer. I described this idea in more detail here . Good luck and clean code to you!