I have a function called ll() for creating a linked list as follows. My program requires two linked lists. Is it possible to reuse this function so I can have two linked lists, say head1 and head2?
#include <stdio.h>
#include <malloc.h>
typedef struct node
{
int data;
struct node* link;
} Node;
Node* head = NULL;
Node* previous = NULL;
int main(void)
{
ll();
print();
return 0;
}
int ll()
{
int data = 0;
while(1)
{
printf("Enter data, -1 to stop: ");
scanf("%d", &data);
if(data == -1)
break;
addtoll(data);
}
}
int addtoll(int data)
{
Node* ptr = NULL;
ptr = (Node*)malloc(sizeof(Node));
ptr->data = data;
ptr->link = NULL;
if(head == NULL)
head = ptr;
else
previous->link = ptr;
previous = ptr;
}
int print()
{
printf("Printing linked list contents: ");
Node* ptr = head;
while(ptr)
{
printf("%d ", ptr->data);
ptr = ptr->link;
}
printf("\n");
}
Is there a better way than doing something like
main()
{
ll(1);
ll(2);
}
int ll(int serial)
{
if (serial == 1)
Use head1 everywhere in this function
else if(serial == 2)
Use head2 everywhere in this function
}
Instead of passing an int you could also just pass the linked list.
Node head1;
Node head2;
Node previous1;
Node previous2;
int main(){
ll(&head1, &previous1);
ll(&head2, &previous2);
}
int ll(Node* head, Node* previous)
{
int data = 0;
scanf("%d",&data);
*head = {data, null};
previous = head;
while(1)
{
printf("Enter data, -1 to stop : ");
scanf("%d",&data);
if(data == -1)
break;
addtoll(data, previous);
}
}
int addtoll(int data, Node* previous)
{
struct student newNode = {data, null}
previous->link = &newNode;
previous = &newNode;
}
Exceutable Code to implement more than 1 Linked List by appending new node one by one.
Related
I am a beginner to C and am learning linked lists. I tried making functions to have everything organised but no matter what i do the function print_list doesn't print the values. The output is only START and END. I noticed that if I put the same block of code directly into the function that builds the lists, then it prints correctly. What am I doing wrong? (Also first time asking on stack overflow)
Thank you to whoever answers.
#include <stdlib.h>
#include <stdio.h>
typedef struct nd
{
int val;
struct nd *next;
} node;
typedef node * Lista;
void print_list(node*currnode)
{
printf("START -> ");
while (currnode != NULL)
{
printf("%d -> ", currnode->val);
currnode = currnode->next;
}
printf("END");
}
//reimpilista means "buildlist"
node*riempilista(Lista lis){
node *currentNode, *temp;
int i,n;
printf("how many nodes?\n");
scanf("%d",&n);
for (i = 0; i < n; i++)
{
currentNode = (node *)malloc(sizeof(node));
printf("Enter element %d : ", (i + 1));
scanf("%d", ¤tNode->val);
if (i == 0)
{
temp = currentNode;
}
else
{
temp->next = currentNode;
temp = currentNode;
}
}
temp->next = NULL;
return lis;
}
int main(){
Lista listautente=NULL;
listautente=riempilista(listautente);
print_list(listautente);
return 0;
}
When you build the list you need to return the head of the list as a result. So you need to store the pointer to the first node. Then when adding a new node you need to know the previous node, so you need to store it as well. The last added node should have next field poiting to NULL otherwise you won't be able to determine the end of the list and will get an exception.
Here is your code slightly edited.
#include <stdlib.h>
#include <stdio.h>
typedef struct nd {
int val;
struct nd *next;
} node;
typedef node *Lista;
void print_list(node *currnode) {
printf("START -> ");
while (currnode != NULL) {
printf("%d -> ", currnode->val);
currnode = currnode->next;
}
printf("END");
}
//reimpilista means "buildlist"
node *riempilista() {
node *firstNode = NULL, *currentNode = NULL, *previousNode = NULL;
int i, n;
printf("how many nodes?\n");
scanf("%d", &n);
for (i = 0; i < n; ++i) {
currentNode = (node *)malloc(sizeof(node));
printf("Enter element %d : ", (i + 1));
scanf("%d", ¤tNode->val);
currentNode->next = NULL;
if (i == 0) {
firstNode = currentNode;
}
if (previousNode != NULL) {
previousNode->next = currentNode;
}
previousNode = currentNode;
}
return firstNode;
}
int main() {
Lista listautente = riempilista();
print_list(listautente);
return 0;
}
I tried to fix your program with minimal changes. Here it is:
Change
node *currentNode, *temp;
to
node *currentNode, *temp, *head;
Change
temp = currentNode;
to
temp = currentNode; head = temp;
Change
return lis;
to
return head;
Here is the link to the modified code:
https://onlinegdb.com/8cjqifgl2
I'm trying to print the linked list to which I prompt for user input.
This code below is not printing the whole list, only the last element at a time.
I don't seem to find the bug. Can you please take a look at it?
#include <stdio.h>
#include <stdlib.h>
struct Node {
int data;
struct Node *next;
};
struct Node *head;
void Insert(int x) {
struct Node *temp = (struct Node *)malloc(sizeof(struct Node));
temp->data = x;
temp->next = NULL;
head = temp;
};
void Print() {
struct Node *temp = head;
printf("Linked list is: ");
while (temp != NULL) {
printf("%d ", temp->data);
temp = temp->next;
}
printf("\n");
};
int main() {
head = NULL;
int i, x;
for (i = 1; i <= 10; i++) {
if (i == 1) {
printf("Enter 1st number: \n");
} else if (i == 2) {
printf("Enter 2nd number: \n");
} else {
printf("Enter %dth number: \n", i);
}
scanf("%d", &x);
Insert(x);
Print();
}
}
temp->next = NULL; is the culprit. It should be temp->next = head;.
Another (more cornercase) issue is that your code fails to check for errors in malloc and scanf.
Edit in response to comment:
If you want to append (as opposed to prepend), you'll need to keep a tail pointer for forward traversal and then either use a dummy first node (avoids a branch) or special-case an insert to an empty list.
Example of both (with simplistic error handling via exit(1)) in one piece of code:
#include <stdio.h>
#include <stdlib.h>
struct Node {
int data;
struct Node *next;
};
#define DUMMYFIRST 1 //change to 0 to compile the other variant
#if DUMMYFIRST
struct Node dummyfirst;
struct Node *head=&dummyfirst;
#else
struct Node *tail,*head=0;
#endif
void Insert(int x) {
struct Node *newnode = malloc(sizeof(struct Node));
//don't cast the result of malloc in C
//https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc
if(!newnode) { perror("malloc"); exit(1); }
newnode->data = x;
newnode->next = 0;
#if !DUMMYFIRST
if(!tail) tail = head = newnode;
else head->next = newnode;
#else
head->next = newnode;
#endif
head = newnode;
};
void Print() {
#if DUMMYFIRST
struct Node *newnode = dummyfirst.next;
#else
struct Node *newnode = tail;
#endif
printf("Linked list is: ");
while (newnode != NULL) {
printf("%d ", newnode->data);
newnode = newnode->next;
}
printf("\n");
};
int main() {
int i, x;
for (i = 1; i <= 10; i++) {
if (i == 1) {
printf("Enter 1st number: \n");
} else if (i == 2) {
printf("Enter 2nd number: \n");
} else {
printf("Enter %dth number: \n", i);
}
if(1!=scanf("%d", &x)) exit(1);
Insert(x);
Print();
}
}
A more library friendly approach to handling errors would be to propagate the error to the caller, i.e., instead of exiting with an error message right away, you'd change the return value from void to something indicating the error, e.g. so that the caller could check and decide what to do (print it, print it in a localized version, try a different algorithm...)
E.g.:
struct Node *Insert(int x) {
struct Node *newnode = malloc(sizeof(struct Node));
//don't cast the result of malloc in c
//https://stackoverflow.com/questions/605845/do-i-cast-the-result-of-malloc
if(!newnode) return NULL;
//...
};
//...
//calling code:
if(!Insert(x)) perror("Insert"),exit(1);
When you insert the new node, you do not link the rest of the list, instead of temp->next = NULL; you should write
temp->next = head;
To ensure defined behavior, you should check for memory allocation failure and invalid input.
Also remove the dummy ; after the function bodies.
Here is a modified version:
#include <stdio.h>
#include <stdlib.h>
struct Node {
int data;
struct Node *next;
};
struct Node *head;
int Insert(int x) {
struct Node *temp = malloc(sizeof(*temp));
if (temp) {
temp->data = x;
temp->next = head;
head = temp;
return 1;
} else {
return 0;
}
}
void Print(void) {
struct Node *temp = head;
printf("Linked list is: ");
while (temp != NULL) {
printf("%d ", temp->data);
temp = temp->next;
}
printf("\n");
}
int main() {
static char suffix[4][3] = { "th", "st", "nd", "rd" };
int i, x;
for (i = 1; i <= 10; i++) {
int suff = (i >= 1 && i <= 3) ? i : 0;
printf("Enter %d%s number:\n", i, suffix[suff]);
if (scanf("%d", &x) != 1) {
fprintf(stderr, "invalid or missing input\n");
break;
}
if (!Insert(x)) {
fprintf(stderr, "cannot allocate memory for Node\n");
return 1;
}
Print();
}
return 0;
}
I made some polynomial code with a doubly-linked list. for example, if
you write 1 and 2 then 1 is a degree and 2 is coefficient. 1x^2 insert
to doubly linked list. the problem is that when I check my code, the Node
head->degree is changing. if I write 1x^2 then head->degree is 1 next,
I write 2x^1 then head-> degree should maintain 1 but head-> degree
change to 2 I think there is some problem in the head pointer.
#include <stdio.h>
#include <stdlib.h>
// struct
struct Node {
int degree;
int coefficient;
struct Node* next;
struct Node* prev;
};
// global variables
int de; // degree
int co; // coefficient
int flag;
Node** head = (Node**)malloc(sizeof(Node)); //
Node** head1 = (Node**)malloc(sizeof(Node)); //
Node** head2 = (Node**)malloc(sizeof(Node)); //
Node** head3 = (Node**)malloc(sizeof(Node)); //
Node* newNode = (Node*)malloc(sizeof(Node)); //
// function
Node* inputpoly(void);
void printNode(Node* inp);
Node* multiply(Node* a, Node* b);
// main
int main() {
// head null
(*head1) = NULL;
(*head2) = NULL;
(*head3) = NULL;
while (1) {
printf("Input (degree) (coefficient) : ");
scanf_s("%d %d", &de, &co);
if (de * co < 0) { continue; }
if (de < 0 && co < 0) {
printf("Done!\n");
break;
}
*head = inputpoly();
}
printNode(*head);
//multiply(*head1, *head2);
free(head1);
free(head2);
free(head3);
free(newNode);
free(head);
}
Node* inputpoly(void) {
// create Node
newNode->degree = de;
newNode->coefficient = co;
newNode->next = NULL;
newNode->prev = NULL;
// case1
if (flag == 0) {
// list
if ((*head1) == NULL) {
*head1 = newNode;
}
// list x
else {
Node* horse = (*head1);
// front of head
// ------------------There is some problem
printf("%d\n", 1);
printf("--%d\n", newNode->degree);
printf("--%d\n", horse->degree);
if (horse->degree > newNode->degree) {
newNode->next = horse;
horse->prev = newNode;
*head1 = newNode;
}
// barward of head
else {
int num = 0;
while (horse->next != NULL) {
horse = horse->next;
if (horse->degree > newNode->degree) {
horse->prev->next = newNode;
newNode->next = horse;
newNode->prev = horse->prev;
horse->prev = newNode;
num = 1;
break;
}
}
// behind tail
if (num == 0) {
horse->next = newNode;
newNode->prev = horse;
}
}
}
return *head1;
}
}
void printNode(Node* inp) {
Node* horse = inp;
if (horse == NULL)
{
return;
}
while (horse != NULL) {
if (horse->prev == NULL) {
if (horse->degree == 1) {
printf("%d", horse->coefficient);
}
else {
printf("%d x^%d", horse->coefficient, horse->degree);
}
}
else {
if (horse->degree == 1) {
printf(" + %d", horse->coefficient);
}
else {
printf(" + %d x^%d", horse->coefficient, horse->degree);
}
}
}
printf("\n");
}
"i think there is some head pointer problem, and if I fixed it I can this problem. so I want to maintain this code as possible. I want some
advice or solution to my head pointer"
The code posted in your example does not compile:
Before you can fix a head pointer problem the code must compile. This list of errors is detailing 2 things:
first, functions cannot be called outside of a function, eg:
Node** head = (Node**)malloc(sizeof(Node)); //
Node** head1 = (Node**)malloc(sizeof(Node)); //
Node** head2 = (Node**)malloc(sizeof(Node)); //
Node** head3 = (Node**)malloc(sizeof(Node)); //
Node* newNode = (Node*)malloc(sizeof(Node)); //
should be called from within main(void){...} or some other function.
second, every occurrence of Node should be prepended with struct. eg:
struct Node** head = malloc(sizeof(struct Node *));
(have also removed the cast, and modified the size of what you are creating memory for, i.e. a pointer)
Rather then fix these and other problems, here is an example of a doubly linked list that can demonstrate the structure of a simple working program. You can adapt the following to match your needs:
struct Node {
int deg;
int coef;
struct Node* next; // Pointer to next node in DLL
struct Node* prev; // Pointer to previous node in DLL
};
void inputpoly(struct Node** head_ref, int deg, int coef)
{
//allocate node
struct Node *new_node = malloc(sizeof(*new_node));
//assign data
new_node->deg = deg;
new_node->coef = coef;
//set next as new head and prev to null
new_node->next = (*head_ref);
new_node->prev = NULL;
//change prev of head to new */
if ((*head_ref) != NULL)
(*head_ref)->prev = new_node;
//point head to the new node */
(*head_ref) = new_node;
}
void printList(struct Node* node)
{
struct Node* last;
printf("\nread forward\n");
while (node != NULL) {
printf(" %d,%d ", node->deg,node->coef);
last = node;
node = node->next;
}
printf("\nread reverse\n");
while (last != NULL) {
printf(" %d,%d ", last->deg,last->coef);
last = last->prev;
}
}
int main(void)
{
//start with empty list
struct Node* head = NULL;
//create and populate new nodes
inputpoly(&head, 7, 2);
inputpoly(&head, 1, 4);
inputpoly(&head, 4, 6);
//ouput list
printList(head);
getchar();
return 0;
}
Note that this code is offered as a basic demonstration of creating doubly linked list, and illustrate how to traverse both directions. Because it does not free allocated memory, it is not recommended that it be used for any production purpose without addressing that omission.
I want an array of linked List and obviously each linked should have separate head node. Initially, as an example, I am starting with one array element. I am storing linkedlist into current[0] . But it is giving segmentation fault. If I use Node *current it will create a list and working fine. But, I want to store the list within array. What is wrong with the code ?
#include <stdio.h>
#include <stdlib.h>
typedef struct Node {
int data;
struct Node *next;
} Node;
Node *current[20];
void insert_beg_of_list(Node *current[0], int data);
void print_list(Node *current[0]);
void insert_beg_of_list(Node *current[0], int data) {
//keep track of first node
Node *head = current[0];
while(current[0]->next != head) {
current[0] = current[0]->next;
}
current[0]->next = (Node*)malloc(sizeof(Node));
current[0] = current[0]->next;
current[0]->data = data;
current[0]->next = head;
}
void print_list(Node *current[0]) {
Node *head = current[0];
current[0] = current[0]->next;
while(current[0] != head){
printf(" %d ", current[0]->data);
current[0] = current[0]->next;
}
}
int main() {
Node *head = (Node *)malloc(sizeof(Node));
head->next = head;
int data = 0 ;
int usr_input = 0;
int i;
int m;
int j;
scanf("%d", &usr_input);
for (i=0; i<usr_input; i++) {
scanf("%d", &data);
insert_beg_of_list(head, data);
}
printf("The list is ");
print_list(head);
printf("\n\n");
return 0;
}
I think you have mixed the global array current's use. Change your code to this :
#include <stdio.h>
#include <stdlib.h>
typedef struct Node {
int data;
struct Node *next;
} Node;
void insert_beg_of_list(Node *current, int data);
void print_list(Node *current);
void insert_beg_of_list(Node *current, int data) {
//keep track of first node
Node *head = current;
while(current->next != head) {
current = current[0]->next;
}
current->next = malloc(sizeof(Node));
if (current->next == NULL)
return;
current = current->next;
current->data = data;
current->next = head;
}
void print_list(Node *current) {
Node *head = current;
current = current->next;
while(current != head){
printf(" %d ", current->data);
current = current->next;
}
}
int main() {
Node *current[20];
Node *head = malloc(sizeof(Node));
if (head == NULL)
return;
head->next = head;
int data = 0 ;
int usr_input = 0;
int i;
int m;
int j;
scanf("%d", &usr_input);
for (i = 0; i < usr_input; i++) {
scanf("%d", &data);
insert_beg_of_list(head, data);
}
//assign the newly created pointer to a place in the array
current[0] = head;
printf("The list is ");
print_list(head);
printf("\n\n");
return 0;
}
Keep in mind that the parameter current in your functions' prototypes and declarations is not the same as the array current created in your main function. I just left the name as it was.
NOTE : You should do something with head->next pointer, initialize it.
Also read this link on why not to cast the result of malloc and another one on why you should check its result.
You probably want this:
#include <stdio.h>
#include <stdlib.h>
typedef struct Node {
int data;
struct Node *next;
} Node;
void insert_beg_of_list(Node *current, int data);
void print_list(Node *current);
void insert_beg_of_list(Node *current, int data) {
//keep track of first node
Node *head = current;
while (current->next != head) {
current = current->next;
}
current->next = (Node*)malloc(sizeof(Node));
current = current->next;
current->data = data;
current->next = head;
}
void print_list(Node *current) {
Node *head = current;
current = current->next;
while (current != head) {
printf(" %d ", current->data);
current = current->next;
}
}
Node *NewList()
{
Node *newnode = (Node *)malloc(sizeof(Node));
newnode->next = newnode;
}
int main() {
Node *arrayofheads[20];
// We are using only arrayofheads[0] in this example
arrayofheads[0] = NewList();
int data = 0;
int usr_input = 0;
int i;
scanf("%d", &usr_input);
for (i = 0; i<usr_input; i++) {
scanf("%d", &data);
insert_beg_of_list(arrayofheads[0], data);
}
printf("The list is ");
print_list(arrayofheads[0]); printf("\n\n");
return 0;
}
Using double pointers first time to create and display linked list
#include "stdio.h"
#include "stdlib.h"
struct node
{
int data;
struct node * next;
};
void Insert(struct node **, int , int );
void display(struct node *);
int main()
{
int c, data, position;
struct node* head;
do{
printf("Enter a choice :\n");
printf("1. Add an element.\n");
printf("2. Del an element.\n3.Display List.\n");
printf("4.Delete linked list.\n5.Exit.\n");
printf("Your Choice :");
scanf("%d",&c);
switch(c){
case 1 :
printf("\nEnter data and position :\n");
scanf("%d %d",&data,&position);
Insert(&head,data,position);
break;
case 2 :
break;
case 3 :
printf("Linked List : \n");
display(head);
break;
case 4 :
break;
case 5 :
exit(0);
default :
printf("Invalid Choice.\n");
break;
}
}while(1);
return 0;
}
void Insert(struct node **ptrhead, int item, int position){
struct node *p,*newnode;
//node creation.
newnode = (struct node *)malloc(sizeof(struct node));
if (!newnode)
{
printf("Memory Error.\n");
return;
}
newnode->next = NULL;
newnode->data = item;
p = *ptrhead;
// Creates initial node
if (!(p->data))
{
p = newnode;
}
// insertion at beginning
if (position==1)
{
newnode->next = p;
p = newnode;
free(newnode);
}
// insertionn at middle or end.
else
{
int i=1;
while(p->next!=NULL && i<position-1){
p=p->next;
i++;
}
newnode->next = p->next;
p->next = newnode;
}
*ptrhead = p;
};
// Display Linked list
void display(struct node *head){
if (head)
{
do{
printf("%d\n", head->data);
head = head->next;
}while(head->next);
}
};
I will add functions for deletion and other operations later. Right now , I just want to insert and display fns to work . But output comes as infinitely running loop with wrong values. I cannot figure out what's wrong in my code , please help ?
Thanks in advance.
Not sure why somebody would be writing this type of C today, looks like maybe I'm doing your homework for you... In any case, you asked to fix your code, not rewrite it, so here's the minimum set of changes.
head should be initialized to NULL.
if (!(p->data)) is not right. That if statement should just be:
// Creates initial node
if (!p)
{
*ptrhead = newnode;
return;
}
Remove free(newnode);.
The insert at middle/end code could be
int i = 1;
struct node *n = p;
while (n->next != NULL && i<position - 1){
n = n->next;
i++;
}
newnode->next = n->next;
n->next = newnode;
The final insert function:
void Insert(struct node **ptrhead, int item, int position)
{
struct node *p, *newnode;
//node creation.
newnode = (struct node *)malloc(sizeof(struct node));
if (!newnode)
{
printf("Memory Error.\n");
return;
}
newnode->next = NULL;
newnode->data = item;
p = *ptrhead;
// Creates initial node
if (!p)
{
*ptrhead = newnode;
return;
}
// insertion at beginning
if (position == 1)
{
newnode->next = p;
p = newnode;
}
// insertionn at middle or end.
else
{
int i = 1;
struct node *n = p;
while (n->next != NULL && i<position - 1){
n = n->next;
i++;
}
newnode->next = n->next;
n->next = newnode;
}
*ptrhead = p;
}
Your print function isn't quite right, just make it:
// Display Linked list
void display(struct node *head)
{
while (head)
{
printf("%d\n", head->data);
head = head->next;
}
}