Linked List in C using Struct-CodePudding

I am not getting the else part in create_node() function..
As you can see in the else part ,memory block is allocated for r and coeff and power are assigned...but when did they assign r node to the last of linkedlist.. when did they traverse to end of linked list
I mean how is it getting assigned at the last of linked list.


#include <bits/stdc  .h>
using namespace std;

struct Node {
    int coeff;
    int pow;
    struct Node* next;
};

// Function to create new node
void create_node(int x, int y, struct Node** temp)
{
    struct Node *r, *z;
    z = *temp;
    if (z == NULL) {
        r = (struct Node*)malloc(sizeof(struct Node));
        r->coeff = x;
        r->pow = y;
        *temp = r;
        r->next = (struct Node*)malloc(sizeof(struct Node));
        r = r->next;
        r->next = NULL;
    }
    else {
        r->coeff = x;
        r->pow = y;
        r->next = (struct Node*)malloc(sizeof(struct Node));
        r = r->next;
        r->next = NULL;
    }
}

// Display Linked list
void show(struct Node* node)
{
    while (node->next != NULL) {
        printf("%dx^%d", node->coeff, node->pow);
        node = node->next;
        if (node->coeff >= 0) {
            if (node->next != NULL)
                printf(" ");
        }
    }
}

// Driver code
int main()
{
    struct Node *poly1 = NULL, *poly2 = NULL, *poly = NULL;

    // Create first list of 5x^2   4x^1   2x^0
    create_node(5, 2, &poly1);
    create_node(4, 1, &poly1);
    create_node(2, 0, &poly1);

    // Create second list of -5x^1 - 5x^0
    create_node(-5, 2, &poly2);
    create_node(-5, 0, &poly2);

    printf("1st Number: ");
    show(poly1);

    printf("\n2nd Number: ");
    show(poly2);

    return 0;
}

Am I the only one who thinks that create_node() function should be more like this than the above code?

void create_node(int x, int y, struct Node** temp)
{

    struct Node *r, *z;
    z = *temp;
    if (z == NULL) {
       r = (struct Node*)malloc(sizeof(struct Node));
        r->coeff = x;
        r->pow = y;
        r->next=NULL;
        *temp = r;
    }
    else {
        r = (struct Node*)malloc(sizeof(struct Node));
        r->coeff = x;
        r->pow = y;
        r->next=NULL;
        while(z->next!=NULL)
        {
            z=z->next;
        }
        z->next=r;
    }
}

I really want to know how is it producing the right output, even without assigning newnode to last of linked list

CodePudding user response：

If you are going to write a C program then use the operator new to allocate memory instead of calling the C function malloc.

If you want to append a node to the list to its tail then it is better to use a two-sided singly-linked list.

The first function create_node does not make a sense due to appending a dummy node with uninitialized data members except the data member next.

    r->next = (struct Node*)malloc(sizeof(struct Node));
    r = r->next;
    r->next = NULL;

The function show can invoke undefined behavior because it does not check whether the passed pointer is equal to nullptr.

// Display Linked list
void show(struct Node* node)
{
    while (node->next != NULL) {
    //...

The functions as C functions can be declared and defined the following way without using a duplicated code.

void create_node( Node **head, int x, int y )
{
    Node *new_node = new Node { x, y, nullptr };

    while ( *head ) head = &( *head )->next;

    *head = new_node;
}

std::ostream & show( const Node *head, std::ostream &os = std::cout )
{
    for ( ; head != nullptr; head = head->next )
    {
        os << head->coeff << '^' << head->pow;

        if ( head->next != nullptr ) os << "   ";
    }

    return os;
}

CodePudding user response：

I am not getting the else part in create_node() function.. As you can see in the else part ,memory block is allocated for r and coeff and power are assigned...but when did they assign r node to the last of linkedlist.. when did they traverse to end of linked list I mean how is it getting assigned at the last of linked list.

It is not. When you pass a null Node*, z will be null, and your else code is dereferencing r which hasn't even been initialized.

// Function to create new node
void create_node(int x, int y, struct Node** temp)
{
    struct Node *r, *z;
    z = *temp;
    if (z == NULL) {
        r = (struct Node*)malloc(sizeof(struct Node));
        r->coeff = x;
        r->pow = y;
        *temp = r;
        r->next = (struct Node*)malloc(sizeof(struct Node));
        r = r->next;
        r->next = NULL;
    }
    else {
        r->coeff = x;
        r->pow = y;
        r->next = (struct Node*)malloc(sizeof(struct Node));
        r = r->next;
        r->next = NULL;
    }
}

Am I the only one who thinks that create_node() function should be more like this than the above code?

This seems to solve above's code issues. Here you are creating a Node and assigning it to r, then appending it at the end of z (input Node*). Notice though that you are duplicating the code for creating r in both blocks of code. You could take at least that part out of the if-else.

void create_node(int x, int y, struct Node** temp)
{

    struct Node *r, *z;
    z = *temp;
    if (z == NULL) {
        r = (struct Node*)malloc(sizeof(struct Node));
        r->coeff = x;
        r->pow = y;
        r->next=NULL;

        *temp = r;
    }
    else {
        r = (struct Node*)malloc(sizeof(struct Node));
        r->coeff = x;
        r->pow = y;
        r->next=NULL;

        while(z->next!=NULL)
        {
            z=z->next;
        }
        z->next=r;
    }
}