Why is it not displaying the output? [closed] - c

Closed. This question needs debugging details. It is not currently accepting answers.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
Closed 7 years ago.
Improve this question
I'm trying to write a program where I create new nodes and insert items in there.
My problem is when I want to display the items in all the nodes it's not showing it.
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
#define NULL 0
struct node{
int item;
struct node *next;
}lol;
struct node *head = NULL;
void insertfirst(int ele);
void insertnext(int ele);
void displayelement();
int main()
{
clrscr();
int ele,choice;
printf("Enter element in first node:");
scanf("%d",&ele);
do{
printf("Please select any of the other options\n1.Add element to new node\n2.Display elements\n");
scanf("%d",&choice);
switch(choice)
{
case 1:
printf("Enter element in node:");
scanf("%d",&ele);
insertnext(ele);
break;
case 2:
displayelement();
break;
default:
break;
}
getch();
clrscr();
displayelement();
}while(choice < 3);
getch();
return 0;
}
void insertfirst(int ele)
{
struct node *p;
p = (struct node*)malloc(sizeof(struct node));
p -> item = ele;
p -> next = head;
head = p;
}
void insertnext(int ele)
{
struct node *temp;
struct node *p;
temp = head;
p = (struct node*)malloc(sizeof(struct node));
temp = head;
p->item = ele;
p->next = temp ->next;
temp -> next = p;
}
void displayelement()
{
struct node *temp;
temp = head;
printf("\n The nodes are");
while(temp!=NULL)
{
printf("%d",temp -> item);
temp = temp -> next;
}
}
The program seemed to have worked when i did it directly without using switch case
#include<stdio.h>
#include<conio.h>
#include<stdlib.h>
#define NULL 0
struct node{
int item;
struct node *next;
}lol;
struct node *head = NULL;
void insertfirst(int ele);
void insertnext(int ele);
void displayelement();
int main()
{
clrscr();
int ele;
printf("Enter element in first node:");
scanf("%d",&ele);
insertfirst(ele);
insertnext(ele);
displayelement();
getch();
return 0;
}
void insertfirst(int ele)
{
struct node *p;
p = (struct node*)malloc(sizeof(struct node));
p -> item = ele;
p -> next = head;
head = p;
}
void insertnext(int ele)
{
struct node *temp;
struct node *p;
temp = head;
p = (struct node*)malloc(sizeof(struct node));
temp = head;
p->item = ele;
p->next = temp ->next;
temp -> next = p;
}
void displayelement()
{
struct node *temp;
temp = head;
printf("\n The nodes are");
while(temp!=NULL)
{
printf("%d",temp -> item);
temp = temp -> next;
}
}

You forgot to call insertfirst from the new code leading to undefined behavior in insertnext as you dereference a NULL pointer.
Fix the problem by adding
insertfirst(ele);
after
printf("Enter element in first node:");
scanf("%d",&ele);

That looks better:
void insertfirst(int ele)
{
head = (struct node*)malloc(sizeof(struct node));
head->item = ele;
head->next = head;
}
void insertnext(int ele)
{
struct node *p;
p = (struct node*)malloc(sizeof(struct node));
p->item = ele;
p->next = head->next;
head->next = p;
}

Related

Segmentation fault in linked list program (c language)

I'm trying to write a code for linked lists using c++. Insert at begin and Insert at end are not working for some reason. Here is the code.
`
#include<stdio.h>
#include<stdlib.h>
#include<conio.h>
void insertAtBeginning(int );
void insertAtEnd(int );
void printLL();
struct Node
{
int data;
struct Node *link;
};
struct Node *head;
int main()
{
struct Node *temp, *newnode;
int ch=1, i=1, info;
head = NULL;
while(ch)
{
printf("Enter data: ");
scanf("%d", &info);
newnode = (struct Node *)malloc(sizeof(struct Node));
newnode->data = info;
newnode->link = NULL;
if(head == NULL)
{
head = newnode;
temp = newnode;
}
else
{
temp ->link = newnode;
temp = newnode;
}
printf("You wish to continue? (press 0 to terminate)\n");
scanf("%d",&ch);
if(!ch)
{
break;
}
}
temp = head;
while(temp!=NULL)
{
printf("%d -> ",temp->data);
temp = temp->link;
}
printf("\n");
insertAtBeginning(50);
insertAtEnd(150);
//printLL();
}
void insertAtBeginning(int info)
{
struct Node *newnode;
newnode->data = info;
printf("\n%d\n", newnode ->data);
newnode->link = head;
head = newnode;
}
void insertAtEnd(int info)
{
struct Node *temp, *newnode;
newnode->link = NULL;
newnode->data = info;
temp = head;
while(temp!=NULL)
{
temp = temp->link;
}
temp->link = newnode;
printf("\n%d\n", newnode -> data);
}
void printLL()
{
struct Node *temp;
temp = head;
while(temp!=NULL)
{
printf("%d -> ",temp->data);
temp = temp->link;
}
}
`
The problem is somewhere around newnode->data = info in the functions.
I created two functions, one to insert an element at beginning and one to insert an element at end. In both of them, i've created a newnode. The problem is I cannot insert data into those nodes.
When you want to append a new node to the end of a linked list, you must find your last node (a node which its link is NULL, not itself). Also, it is better to use meaningful variable name (temp is too general name). You also forgot to malloc new nodes in insertAtBeginning and insertAtEnd functions. I've fixed these issues in the following code
#include<stdio.h>
#include<stdlib.h>
void insertAtBeginning(int );
void insertAtEnd(int );
void printLL();
struct Node
{
int data;
struct Node *link;
};
struct Node *head = NULL;
int main()
{
struct Node *it, *newnode, *tail;
int ch=1, i=1, info;
while(ch){
printf("Enter data: ");
scanf("%d", &info);
newnode = malloc(sizeof(struct Node));
newnode->data = info;
newnode->link = NULL;
if (head == NULL) {
head = newnode;
tail = newnode;
} else {
tail->link = newnode;
tail = newnode;
}
printf("You wish to continue? (press 0 to terminate, else to continue)\n");
scanf("%d",&ch);
if(ch == 0) {
break;
}
}
it = head;
while(it != NULL) {
printf("%d -> ",it->data);
it = it->link;
}
printf("\n");
insertAtBeginning(50);
insertAtEnd(150);
}
void insertAtBeginning(int info)
{
struct Node *newnode;
newnode = malloc(sizeof(struct Node));
newnode->data = info;
printf("\n%d\n", newnode->data);
newnode->link = head;
head = newnode;
}
void insertAtEnd(int info)
{
struct Node *it, *newnode;
newnode = malloc(sizeof(struct Node));
newnode->link = NULL;
newnode->data = info;
it = head;
while(it->link != NULL)
{
it = it->link;
}
it->link = newnode;
printf("\n%d\n", newnode->data);
}
void printLL()
{
struct Node *it;
it = head;
while(it!=NULL)
{
printf("%d -> ",it->data);
it = it->link;
}
}
You're treating your uninitialized stack variable (struct Node *newnode) as a pointer to a struct Node and trying to update its fields:
struct Node *newnode;
newnode->data = info;
This doesn't work because the value of newnode is whatever garbage was on the stack beforehand, and trying to deref it (*newnode) will likely give a seg fault since you're trying to read from some unknown memory address.
Notice how inside main, you assign a result from malloc to newnode, this means you know that (given that malloc didn't return NULL), the pointer is valid, and you're free to use the memory it points to.

Error: in creation of Linked List Display function

I am trying to create a linked list with display() function in it but i continuously getting error in it. a function not able to display element in output.
I have try various online solution of code but not worked on my code.
Below is my code if anyone have any idea. let me tell to solve it
#include <stdio.h>
#include <stdlib.h>
struct node{
int data;
struct node *next;
};
int create(int n){
int d1,d2,i;
struct node *head, *temp, *newnode;
head = (struct node *) malloc(sizeof(struct node));
printf("enter the data for node 1");
scanf("%d",&d1);
head->data = d1;
head->next = NULL;
temp = head;
for(i=2; i<=n; i++){
newnode = (struct node *)malloc(sizeof(struct node));
printf("enter a data for %d node",i);
scanf("%d",&d2);
newnode->data = d2;
newnode->next = NULL;
temp->next = newnode;
temp = temp->next; // newnode can also use instead of temp->next
}
void printList(struct node* node) {
while (node != NULL) {
printf(" %d ", node->data);
node = node->next;
}
}
}
int main()
{
struct node* head = NULL;
int n;
printf("Enter number of node to create");
scanf("%d",&n);
create(n);
printList(head);
return 0;
}
Change return type of the create function to return the address of the node like this: struct node * create(int n) and change return value to: return head;.
Finally, in main() save the returned address in head pointer: head = create(n);

Linked List not printing

I am trying to create a simple linked list using C, I think I was able to construct the linked list itself, but when I try and print it, it prints the value of the last node instead of all the values in the list.
#include <stdio.h>
#include <alloca.h>
typedef int DATA;
struct Node
{
DATA d;
struct Node *next;
};
void printList(struct Node **head)
{
struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
struct Node *temp;
temp = *head;
while(temp!=NULL)
{
printf("%d \n", temp->d);
temp = temp->next;
}
}
int main()
{
struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
struct Node *head = newNode;
struct Node *temp = newNode;
head->d = 1;
int i = 0;
printf("Enter 3 numbers");
for( i = 0; i< 3; i++)
{
scanf("%d", &temp->d);
temp->next = newNode;
temp = temp->next;
}
temp->next = NULL;
printf("%d \n", temp->d);
return 0;
}
Any help/tips would be greatly appreciated.
There are multiple problems in your code:
You are not creating the list properly. You are allocating memory for only one node and playing around with pointers improperly causing the linked list to be pointed to the same memory
You are not calling printList function at all
It is not clear why you are allocating memory again in printList whereas it should be printing the already created list
Also, no need to pass double pointer for printList as you are not modifying the list.
Though you should be understanding and doing the changes yourself, I am providing a below modified program which I hope will help you understand the mistakes in your code.
Please see the below modified version of the code
#include<stdio.h>
#include <alloca.h>
typedef int DATA;
struct Node
{
DATA d;
struct Node *next;
};
void printList(struct Node *head)
{
struct Node *temp = head;
while(temp!=NULL)
{
printf("%d \n", temp->d);
temp = temp->next;
}
}
struct Node *createNode()
{
struct Node *newNode;
newNode = malloc(sizeof(struct Node));
if (NULL == newNode)
return NULL;
memset(newNode, 0, sizeof(struct Node));
return newNode;
}
int main()
{
struct Node *newNode = NULL;
struct Node *headNode = NULL;
struct Node *temp = NULL;
int i = 0;
int data = 0;
printf("Enter 3 numbers\n");
for( i = 0; i< 3; i++)
{
scanf("%d", &data);
newNode = createNode();
if (NULL == newNode)
break;
newNode->d = data;
if (headNode == NULL)
{
headNode = newNode;
temp = newNode;
}
else
{
temp->next = newNode;
temp = temp->next;
}
}
printList(headNode);
return 0;
}
Replace your code with the following code :-
#include<stdio.h>
#include <alloca.h>
typedef int DATA;
struct Node
{
DATA d;
struct Node *next;
};
void printList(struct Node **head)
{
struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
struct Node *temp;
temp = *head;
while(temp->next!=NULL)
{
printf("%d \n", temp->d);
temp = temp->next;
}
}
int main()
{
struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
struct Node *head = newNode;
struct Node *temp = newNode;
head->d = 1;
int i = 0;
printf("Enter 3 numbers");
for( i = 0; i< 3; i++)
{
struct Node *newNode = (struct Node *)malloc(sizeof(struct Node));
scanf("%d", &temp->d);
temp->next = newNode;
temp = temp->next;
}
printList(head);
return 0;
}
Here you need to declare the newNode in the loop also while taking the input. As, the current value is over-writted, the old value is lossed and only the value of last node is printed.
Also while printing, check for temp->next!=Null instead of temp!=NULL

linked list using double pointers

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;
}
}

inserting an element in a linked list

Considering a linked list containing five elements.
1,2,3,4,5 a no '7' is to be inserted after two. we will have an head pointing to the first element of the linked list and ptr at the last. while inserting an element before 3 we will loop through the linked list starting from head to last and we will introduce another pointer(prev) to hold the previous pointers address.ptr will point to the current node and if a matching data is found(3) then we have to include the new node between 2 and 3.
We can do it as we have previous pointer.How to do it without using a previous pointer.
EDITED:
#include<stdio.h>
#include<stdlib.h>
struct list
{
int data;
struct list* link;
};
struct list *head=NULL;
struct list *tail=NULL;
void createList(int value);
void displayList(struct list* head_node);
void insertNewNode();
int value;
int main()
{
int i;
for(i=0;i<5;i++)
{
printf("\nEnter the data to be added into the list:\n");
scanf("%d",&value);
createList(value);
}
printf("\nCreated Linked list is\n");
//displayList(head);
printf("\nInsert a node\n");
insertNewNode();
displayList(head);
return 0;
}
void insertNewNode()
{
int val;
struct list* ptr=NULL,*new_node,*prev=NULL;
new_node = (struct list*)malloc(sizeof(struct list));
printf("Enter the data to be inserted!");
scanf("%d",&val);
for(ptr=head;ptr;ptr=ptr->link)
{
if(ptr->data == 3)
{
printf("Found");
new_node->data = val;
prev->link=new_node;
new_node->link = ptr;
}
prev = ptr;
}
}
void createList(int value)
{
struct list *newNode;
newNode = (struct list*)malloc(sizeof(struct list));
//tail = (struct list*)malloc(sizeof(struct list));
newNode->data = value;
if(head == NULL)
{
head = newNode;
}
else
{
tail->link = newNode;
}
tail = newNode;
tail->link = NULL;
}
void displayList(struct list *head_node)
{
struct list *i;
for(i=head;i;i=i->link)
{
printf("%d",i->data);
printf(" ");
}
printf("\n");
}
void insertNewNode()
{
int val;
struct list* ptr=NULL,*new_node;
new_node = (struct list*)malloc(sizeof(struct list));
printf("Enter the data to be inserted!");
scanf("%d",&val);
for(ptr=head;ptr;ptr=ptr->link)
{
if(ptr->data == 2)
{
printf("Found");
new_node->data = val;
new_node->link = ptr->link;
ptr->link = new_node;
}
}
}
Update:
This is probably what you want:
void insertNewNode()
{
int val;
struct list* ptr=NULL,*new_node;
new_node = (struct list*)malloc(sizeof(struct list));
printf("Enter the data to be inserted!");
scanf("%d",&val);
for(ptr=head;ptr->link;ptr=ptr->link)
{
if(ptr->link->data == 3)
{
printf("Found");
new_node->data = val;
new_node->link = ptr->link;
ptr->link = new_node;
}
}
}
Here:
if(ptr->link->data == 3)
you simply look ahead to check if next node has value that you need.
Let's call curr the pointer at the current element, next the pointer at the next element, and value the number stored.
Traverse the list until curr.value == 2, now just create a new_node with new_node.value = 7 and set new_node.next = curr.next and curr.next = new_node

Resources