Creating an entire doubly linked list in one function-CodePudding

I'm new to DSA and currently learning linked-list. I was trying to create an entire linked list in one function. The first scanf in createList function doesn't seem to assign the input to the address provided(i.e. &n). I tried printing n right after scanf. It doesn't print n to console at all. As a result, the output is not the way I expected. I can't figure out why.

//ENTIRE CODE HERE

#include<stdio.h>
#include<stdlib.h>
struct node {
    struct node* prev;
    int data;
    struct node* next;
};

void print_nodes(struct node* );
struct node* addToEmpty(struct node*, int);
struct node* addAtEnd(struct node*, int);
struct node* createList(struct node*);

int main() {
    struct node* head = NULL;
    head = createList(head);
    print_nodes(head);
}

void print_nodes(struct node* head) {
    struct node* ptr = head;
    while (ptr != NULL) {
        printf("%d ", ptr->data);
        ptr = ptr->next;
    }
    printf("\n");
}

struct node* addToEmpty(struct node* head, int data) {
    struct node* temp = malloc(sizeof(struct node));
    temp->prev = NULL;
    temp->data = data;
    temp->next = NULL;
    head = temp;
    return head;
}

struct node* addAtEnd(struct node* head, int data) {
    struct node* tp = head;
    struct node* temp = malloc(sizeof(struct node));
    temp->prev = NULL;
    temp->data = data;
    temp->next = NULL;
    while (tp->next != NULL) {
        tp = tp->next;
    }
    tp->next = temp;
    temp->prev = tp;
    return head;
}

struct node* createList(struct node* head) {
    int n, data, i;
    printf("Enter the number of nodes: ");
    scanf("%d ", &n);

    if (n == 0)
        return head;

    printf("Enter the element of node 1: ");
    scanf("%d ", &data);
    head = addToEmpty(head, data);

    for (i = 1; i < n; i  ) {
        printf("Enter the element of node %d: ", i   1);
        scanf("%d", &data);
        head = addAtEnd(head, data);
    }
    return head;
}

CodePudding user response：

your problem is so simple , instead of scanf("%d ", &n); , just write scanf("%d", &n); by which I mean to remove the wite space after %d as it's producing some strange behavior in your case , as if you refer to scanf() manual page , they say that :

A sequence of white-space characters (space, tab, newline, etc.; see isspace(3)). This directive matches any amount of white space, including none, in the input.

which is supposed to ignore any whitespace after the number entered till getting a valid char.

and here is the full code but with this only small modification:

    #include<stdio.h>
#include<stdlib.h>
struct node {
    struct node* prev;
    int data;
    struct node* next;
};

void print_nodes(struct node* );
struct node* addToEmpty(struct node*, int);
struct node* addAtEnd(struct node*, int);
struct node* createList(struct node*);

int main() {
    struct node* head = NULL;
    head = createList(head);
    print_nodes(head);
}

void print_nodes(struct node* head) {
    struct node* ptr = head;
    while (ptr != NULL) {
        printf("%d ", ptr->data);
        ptr = ptr->next;
    }
    printf("\n");
}

struct node* addToEmpty(struct node* head, int data) {
    struct node* temp = malloc(sizeof(struct node));
    temp->prev = NULL;
    temp->data = data;
    temp->next = NULL;
    head = temp;
    return head;
}

struct node* addAtEnd(struct node* head, int data) {
    struct node* tp = head;
    struct node* temp = malloc(sizeof(struct node));
    temp->prev = NULL;
    temp->data = data;
    temp->next = NULL;
    while (tp->next != NULL) {
        tp = tp->next;
    }
    tp->next = temp;
    temp->prev = tp;
    return head;
}

struct node* createList(struct node* head) {
    int n, data, i;
    printf("Enter the number of nodes: ");
    scanf("%d", &n);

    if (n == 0)
        return head;

    printf("Enter the element of node 1: ");
    scanf("%d", &data);
    head = addToEmpty(head, data);

    for (i = 1; i < n; i  ) {
        printf("Enter the element of node %d: ", i   1);
        scanf("%d", &data);
        head = addAtEnd(head, data);
    }
    return head;
}

and this is the output:

 Enter the number of nodes:3
 Enter the element of node 1:1
 Enter the element of node 2:2
 Enter the element of node 3:3
 1 2 3

CodePudding user response：

I tried out your code and found issues with the space in the literal string in the "scanf" statements. I see that someone else found that and offered up the solution to that with the cleanup of the "scanf" statements. I would say that if you are to accept an answer, select the first one. However, I just wanted to also offer up my code snippet with a couple of additional tweaks.

#include<stdio.h>
#include<stdlib.h>
struct node
{
    struct node* prev;
    int data;
    struct node* next;
};

void print_nodes(struct node* );
struct node* addToEmpty(struct node*, int);
void addAtEnd(struct node*, int);           /* No requirement for a node to be returned as the pointers are all set up in the function */
struct node* createList(struct node*);

int main()
{
    struct node* head = NULL;
    head = createList(head);
    print_nodes(head);
}

void print_nodes(struct node* head)
{
    struct node* ptr = head;
    while (ptr != NULL)
    {
        printf("%d ", ptr->data);
        ptr = ptr->next;
    }
    printf("\n");
}

struct node* addToEmpty(struct node* head, int data)
{
    struct node* temp = malloc(sizeof(struct node));
    temp->prev = NULL;
    temp->data = data;
    temp->next = NULL;
    //head = temp;
    return temp;        /* Return the pointer to the new struct - no need for update of head here */
}

void addAtEnd(struct node* head, int data)
{
    struct node* tp = head;
    struct node* temp = malloc(sizeof(struct node));
    temp->prev = NULL;
    temp->data = data;
    temp->next = NULL;
    while (tp->next != NULL)
    {
        tp = tp->next;
    }
    tp->next = temp;
    temp->prev = tp;
    return;
}

struct node* createList(struct node* head)
{
    int n, data, i;
    printf("Enter the number of nodes: ");
    scanf("%d", &n);

    if (n == 0)
        return head;

    printf("Enter the element of node 1: ");
    scanf("%d", &data);
    head = addToEmpty(head, data);

    for (i = 1; i < n; i  )
    {
        printf("Enter the element of node %d: ", i   1);
        scanf("%d", &data);
        addAtEnd(head, data);
    }
    return head;
}

First off, since there is not a need to return a "struct" pointer in the function "addAtEnd", I revised that to be a "void" function return signature. Second, in the "addToEmpty" function, one can just return the pointer value in "temp" instead of placing the value into the input parameter "head"; however, it works either way. It is just a matter of choice.

As a sample, here is some output data at the terminal.

@Una:~/C_Programs/Console/CompleteList/bin/Release$ ./CompleteList 
Enter the number of nodes: 4
Enter the element of node 1: 65535
Enter the element of node 2: 2458
Enter the element of node 3: -44
Enter the element of node 4: 3258779
65535 2458 -44 3258779

I would suggest trying out both iterations.