I have more experience with linked lists after gaining practice and support from SO, given my last few questions. Essentially, I am now following an algorithm that will convert an array to a singly linked list.

Algorithm: CONVERT (A, N, HEAD)
1. Set HEAD = NULL
2. Repeat steps 3 to 8 while N ≠ -1
3. Allocated memory for NEW node
4. IF NEW = NULL then Print: “Memory not Available” and Return
5. Set NEW→DATA = A[N-1]
6. Set NEW→LINK = HEAD
7. Set HEAD = NEW
8. Set N = N - 1
[End of loop]
9. Return

I have attempted creating the code for this, however, after printing out the node carrying the data, I get a bunch of zeros. I know that with an array, if I assign a large size to the array and do not fill all values in, then these are assigned 0. However, this is not the case for my example.

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

typedef struct node {
    int DATA;
    struct node* LINK;
} node;

void convert(int A[], int N, node* head){
    head = NULL;
    while(N != -1){
        node* new;
        new = (node*)malloc(sizeof(node));
        if (new == NULL){
            printf("Memory not available");
            return;
        }
        printf("%i", new->DATA);
        new->DATA = A[N-1];
        new->LINK = head;
        head = new;
        N--;
    }
    return;
}

int main(){
    int arr[10] = {0, 1, 2, 3, 4};
    int size = sizeof(arr)/sizeof(arr[0]);
    node* former;
    former = (node*)malloc(sizeof(node));
    convert(arr, size, former);
    return 0;
}

Would print out the following:

00000000000% 

How do I convert the array values to the singly linked list, what might I be missing?

CodePudding user response：

There are a few problems with your code:

1. You don't receive the created list head pointer back to main.
2. You print the data before you assign it and the printing will be inverted if you do during the creation of the list.
3. You don't free the allocated memory and create memory leaks.

Here is how to fix it:

1. Return the created list head pointer from the convert function.
2. Write a separate function for printing the list.
3. Write a function for freeing the memory of the list.

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

typedef struct node
{
    int DATA;
    struct node *LINK;
} node;

node *convert(int A[], int N);
void printList(node *head);
void freeList(node *head);

node *convert(int A[], int N)
{
    node *head = NULL;
    for (int i = N - 1; i >= 0; i--)
    {
        node *new = malloc(sizeof(node));
        if (new == NULL)
        {
            printf("Memory not available");
            freeList(head); // free already allocated memory
            return NULL;
        }
        new->DATA = A[i];
        new->LINK = head;
        head = new;
    }
    return head; // return the head pointer
}

void printList(node *head)
{
    node *current = head;
    while (current != NULL)
    {
        printf("%d ", current->DATA);
        current = current->LINK;
    }
}

void freeList(node *head)
{
    node *current = head;
    node *next = NULL;
    while (current != NULL)
    {
        next = current->LINK;
        free(current);
        current = next;
    }
}

int main()
{
    int arr[5] = {0, 1, 2, 3, 4};
    int size = sizeof(arr) / sizeof(arr[0]);
    node *former = convert(arr, size);
    printList(former);
    freeList(former);
    return 0;
}

CodePudding user response：

Seems you are trying to print new->DATA value before you assign it's value. print it after assigning the value.

And head pointer is a local variable, so it's changes will not be reflected in Main() function. Change head pointer as follows inside Convert() function.

*head = NULL; 

And your Main() function should be updated as follows,

int main(){
    int arr[10] = {0, 1, 2, 3, 4};
    int size = sizeof(arr)/sizeof(arr[0]);
    node* head;
    convert(arr, size, &head);
    return 0;
}

updated:

Change your Convert() function as follows,

void convert(int A[], int N, node ** head) {
  * head = NULL;
  while (N != -1) {
    node * new;
    new = malloc(sizeof new[0]);
    if (new == NULL) {
      printf("Memory not available");
      return;
    }
    new -> DATA = A[N - 1];
    printf("%i", new -> DATA);
    new -> LINK = * head;
    * head = new;
    N--;
  }
  return;
}

CodePudding user response：

Split the problem into smaller bits. Use functions to program them.

typedef struct node {
    int DATA;
    struct node* LINK;
} node;

node *add(node *last, int data)
{
    node *wrk = malloc(sizeof(*wrk));
    if(wrk)
    {
        wrk -> DATA = data;
        wrk -> LINK = NULL;
    }
    if(last) last -> LINK = wrk;
    else last = wrk;
    return wrk;
}

node *convert(int *data, size_t size)
{
    node *head = NULL, *last;
    
    if(data && size) 
    {
        if((head = add(NULL, *data  )))
        {
            last = head;
            while(--size)
            {
                if(!(last = add(last, *data  ))) break;
            }
        }
    }
    return head;
}

void printList(const node *head)
{
    while(head)
    {
        printf("%d\n", head -> DATA);
        head = head -> LINK;
    }
}

int main(void)
{
    int arr[] = {9, 1, 2, 3, 4};
    size_t size = sizeof(arr)/sizeof(arr[0]);

    node *head = convert(arr, size);

    printList(head);
    return 0;
}