The following is a simple code segment in C to create a linked list and print all elements contained in the list.
User is asked to input integer data till a zero is entered which marks the termination of user input; Once data is saved in the linked list, the program prints all elements stored in the list and then completes its execution.
I can't make it run, every time it gives a "Segmentation fault" error, please check and tell me where I'm wrong (using gcc 4.8.2)
Code :
struct node
{
int data;
struct node * next;
};
struct node * createLinkedList()
{
int x;
struct node * start;
start = NULL;
printf("Input 0 to end, Insert elements :\n");
for(scanf("%d", &x); x ;scanf("%d", &x))
{
struct node * temp = (struct node *) malloc(sizeof(struct node));
if (temp)
{
temp->data = x;
temp->next = NULL;
if(start == NULL) {
start = temp;
} else {
start->next = temp;
start = temp;
}
}
}
return start;
}
void printLinkedList(struct node * start)
{
if (start == NULL) {
printf("Linked List is empty!\n");
} else {
printf("\nPrinting Linked List : \n");
struct node * s;
s = start;
while(s != NULL)
{
printf("%d\n", s->data);
s = s->next;
}
}
}
int main(int argc, char const *argv[])
{
struct node * start;
start = NULL;
start = createLinkedList();
printLinkedList(start);
return 0;
}
This part of code
if(start == NULL) {
start = temp;
} else {
start->next = temp;
start = temp;
}
is invalid. There has to be
if(start == NULL) {
start = temp;
} else {
temp->next = start;
start = temp;
}
Also you need to have a function that deletes all nodes of the list.
Related
I am just implementing circular linked list program but in this program i am having to face trouble, as you can see I am going to past code below, when I call insertAtLast and isertAtFirst function it's work fine but as soon as I call viewList function to view list item but it shows "there is no items" which I wrote inside if block for run when last is null but in this program I have already inserted two items before viewList call so I think last should not be null because I have already inserted item, I want to print all items of list by viewList function
#include <stdio.h>
#include <stdlib.h>`
#include <conio.h>
struct node {
int item;
struct node *next;
};
void insertAtFirst(struct node **last, int data) {
struct node *n, *t;
n = malloc(sizeof(struct node));
n->item = data;
t = *last;
if(*last == NULL) {
n->next = n;
t = n;
}
else {
n->next = t->next;
t->next = n;
}
}
void insertAtLast(struct node **last, int data) {
struct node *n, *t;
n = malloc(sizeof(struct node));
n->item = data;
t = *last;
if(*last == NULL) {
n->next = n;
t = n;
}
else {
n->next = t->next;
t->next = n;
t = n;
}
}
void viewList(struct node *last) {
struct node *start;
if(last == NULL)
printf("\n there is no items......");
else {
start = last->next;
while(start->next != last->next) {
printf("%d ", start->item);
start = start->next;
}
}
}
int main(){
struct node *last = NULL;
insertAtLast(&last, 3);
insertAtFirst(&last, 5);
viewList(last);
return 0;
}
You should use *last = n instead of t = n.
And that's because the latter just causes the variable t to point to n and that's it. But by doing *last = n you will at least insert a value in the list even if last == NULL I guess that would give the desired output.
I was tasked with implementing a merge sort algorithm on a list written in C/C++. I have the general idea down, wrote my code and have successfully compiled it. However, when I run it, it will begin fine but then hang on "prepared list, now starting sort" without giving any kind of error. I have tried to look through my code but I am at a complete loss as to what the issue could be. I am also pretty amateurish with debugging, so using gdb to the best of my abilities has lead me no where. Any advice or tips would be a tremendous help, thank you all!
#include <stdio.h>
#include <stdlib.h>
struct listnode
{
struct listnode *next;
int key;
};
//Finds length of listnode
int
findLength (struct listnode *a)
{
struct listnode *temp = a;
int i = 0;
while (temp != NULL)
{
i++;
temp = temp->next;
}
return i;
}
struct listnode *
sort (struct listnode *a)
{
// Scenario when listnode is NULL
if (findLength (a) <= 1)
return a;
//Find middle
int mid = findLength (a) / 2;
struct listnode *temp = a;
struct listnode *first = a;
struct listnode *second;
for (int i = 0; i < mid - 1; i++)
{
temp = a->next;
}
second = temp->next;
temp->next = NULL;
//Recursive calls to sort lists
first = sort (first);
second = sort (second);
if (first != NULL && second != NULL)
{
if (first->key < second->key)
{
a = first;
first = first->next;
}
else
{
a = second;
second = second->next;
}
}
struct listnode *head = a;
struct listnode *tail = a;
while (first != NULL && second != NULL)
{
if (first->key < second->key)
{
tail = first;
first = first->next;
tail = tail->next;
}
else
{
tail = second;
second = second->next;
tail = tail->next;
}
}
if (first == NULL)
{
while (second != NULL)
{
tail = second;
second = second->next;
tail = tail->next;
}
}
while (first != NULL)
{
tail = first;
first = first->next;
tail = tail->next;
}
return a;
}
Here is the test code provided, written in C:int
main (void)
{
long i;
struct listnode *node, *tmpnode, *space;
space = (struct listnode *) malloc (500000 * sizeof (struct listnode));
for (i = 0; i < 500000; i++)
{
(space + i)->key = 2 * ((17 * i) % 500000);
(space + i)->next = space + (i + 1);
}
(space + 499999)->next = NULL;
node = space;
printf ("\n prepared list, now starting sort\n");
node = sort (node);
printf ("\n checking sorted list\n");
for (i = 0; i < 500000; i++)
{
if (node == NULL)
{
printf ("List ended early\n");
exit (0);
}
if (node->key != 2 * i)
{
printf ("Node contains wrong value\n");
exit (0);
}
node = node->next;
}
printf ("Sort successful\n");
exit (0);
}
You're close, but with some silly errors. Check the append operations in the merge step. They're not doing what you think they are. And of course you meant temp = temp->next; in the splitting loop.
If gdb is overwhelming, adding printf's is a perfectly fine way to go about debugging code like this. Actually you want to write a list printing function and print the sublists at each level of recursion plus the results of the merge step. It's fun to watch. Just be neat and delete all that when you're done.
Here's code that works for reference:
struct listnode *sort(struct listnode *lst) {
if (!lst || !lst->next) return lst;
struct listnode *q = lst, *p = lst->next->next;
while (p && p->next) {
q = q->next;
p = p->next->next;
}
struct listnode *mid = q->next;
q->next = NULL;
struct listnode *fst = sort(lst), *snd = sort(mid);
struct listnode rtn[1], *tail = rtn;
while (fst && snd) {
if (fst->key < snd->key) {
tail->next = fst;
tail = fst;
fst = fst->next;
} else {
tail->next = snd;
tail = snd;
snd = snd->next;
}
}
while (fst) {
tail->next = fst;
tail = fst;
fst = fst->next;
}
while (snd) {
tail->next = snd;
tail = snd;
snd = snd->next;
}
tail->next = NULL;
return rtn->next;
}
On my old MacBook this sorts 10 million random integers in a bit over 4 seconds, which doesn't seem too bad.
You can also put the append operation in a macro and make this quite concise:
struct listnode *sort(struct listnode *lst) {
if (!lst || !lst->next) return lst;
struct listnode *q = lst, *p = lst->next->next;
while (p && p->next) {
q = q->next;
p = p->next->next;
}
struct listnode *mid = q->next;
q->next = NULL;
struct listnode *fst = sort(lst), *snd = sort(mid);
struct listnode rtn[1], *tail = rtn;
#define APPEND(X) do { tail->next = X; tail = X; X = X->next; } while (0)
while (fst && snd) if (fst->key < snd->key) APPEND(fst); else APPEND(snd);
while (fst) APPEND(fst);
while (snd) APPEND(snd);
tail->next = NULL;
return rtn->next;
}
Does it have to be a top down merge sort? To get you started, here's a partial fix, didn't check for other stuff. The | if (first != NULL && second != NULL) | check isn't needed since the prior check for length <= 1 takes care of this, but it won't cause a problem.
while (first != NULL && second != NULL)
{
if (first->key < second->key)
{
tail->next = first;
tail = first;
first = first->next;
}
else
{
tail->next = second;
tail = second;
second = second->next;
}
}
if (first == NULL)
{
tail->next = second;
}
else
{
tail->next = first;
}
}
I have a program where three values are inserted into linked lists. When I try to iterate through the list I only get the first value printed. Sorry if the function names are confusing I'm still new to c and I'm trying to use the function and variable names gave me just to make my life easier when taking a test. I'm also pretty unfamiliar with debugger and how I would use it to find out what is going on here. Thanks in advance.
void program_header(char i[]);
Node *allocateNode(int iNewInfo);
Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes);
Node *insertLL(Node **ppHead, int iNewInfo);
void printLL(Node *pHead);
int main(int argc, char *argv[])
{
program_header(argv[0]);
insertLL(&pHead, 84);
insertLL(&pHead, 45);
insertLL(&pHead, 81);
printLL(pHead);
return 0;
}
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
typedef struct Node
{
int iInfo;
struct Node *pNext;
}Node;
Node *pHead = NULL;
Node *pNew = NULL;
Node *pPrecedes = NULL;
Node *allocateNode(int iNewInfo)
{
// to allocate a new node
pNew = malloc(sizeof(Node));
if (pNew == NULL)
printf("Memory allocation error");
pNew->iInfo = iNewInfo;
pNew->pNext = NULL;
return pNew;
}
Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes)
{
Node *p;
for (p = pHead; p != NULL; p = p->pNext)
{
if (iMatch == p->iInfo)
printf("Found! %d\n", iMatch);
return p;
if (iMatch < p->iInfo)
return NULL;
*ppPrecedes = p;
}
return NULL;
}
Node *insertLL(Node **ppHead, int iNewInfo)
{
Node *pFind;
// see if it already exists
pFind = searchLL(*ppHead, iNewInfo, &pPrecedes);
if(pFind != NULL)
return pFind;
// Doesn't already exist. Allocate a node and insert it
pNew = allocateNode(iNewInfo);
if(pPrecedes == NULL)
{ //insert at head
pNew->pNext = *ppHead;
*ppHead = pNew;
}
else
{ //insert after a node
pNew->pNext = pPrecedes->pNext;
pPrecedes->pNext = pNew;
}
return pNew;
}
void printLL(Node *pHead)
{
Node *p;
printf("iInfo Values\n");
for (p = pHead; p != NULL; p = p->pNext)
{
printf("%d\n", p->iInfo);
}
p = pHead;
}
void program_header(char i[])
{
int j, n = strlen(&i[2]);
char *name = &i[2], border[n], dash = '-';
// loads dashes into array
for(j = 0; j < n; j++)
border[j] = dash;
border[j] = '\0';
// print header
printf("\n~%s~\n~%s~\n~%s~\n\n"
, border, name, border);
}
I believe your problem is in your search method. I have reformatted it to show the way that it is currently behaving. To help in making your code more readable and to avoid these type of errors you should get in the habit of using braces in your if statements even if they are only one line.
This is your current code
Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes)
{
Node *p;
for (p = pHead; p != NULL; p = p->pNext)
{
if (iMatch == p->iInfo)
{
printf("Found! %d\n", iMatch);
}
return p;
if (iMatch < p->iInfo)
{
return NULL;
}
*ppPrecedes = p;
}
return NULL;
}
Notice in the for loop that no matter if a match is found or not you are always returning p which is really pHead. Then in your insert code you are checking to see if the item is found in the list. Since you always return head it thinks that the item is in the list and never adds a new item.
I haven't tested this, but I believe this is the change you would need to make. You are expecting the search to return a node if the value is already in the list. So you want to return p if there is a match, otherwise you want to return NULL:
Node *searchLL(Node *pHead, int iMatch, Node **ppPrecedes)
{
Node *p;
for (p = pHead; p != NULL; p = p->pNext)
{
if (iMatch == p->iInfo)
{
printf("Found! %d\n", iMatch);
return p;
}
if (iMatch < p->iInfo)
{
return NULL;
}
*ppPrecedes = p;
}
return NULL;
}
correct this
Node *allocateNode(int iNewInfo)
{
// to allocate a new node
pNew = malloc(sizeof(Node));
if (pNew == NULL)
printf("Memory allocation error");
pNew->iInfo = iNewInfo;
pNew->pNext = NULL;
return pNew;
}
to this
Node *allocateNode(int iNewInfo)
{
// to allocate a new node
pNew = malloc(sizeof(Node));
if (pNew){
pNew->iInfo = iNewInfo;
pNew->pNext = NULL;
}else{
printf("Memory allocation error");
}
return pNew;
}
So here's the code I have at the moment.
#include<stdio.h>
#include<stdlib.h>
#include <string.h>
struct cake {
char name;
int waitTime;
int prepTime;
int bakeTime;
int turnTime;
};
struct cake redVelvet(){
struct cake c;
c.name = "R";
c.waitTime = 0;
c.prepTime = 60;
c.bakeTime = 30;
c.turnTime = 0;
return c;
};
struct Node {
struct cake cake;
struct Node* next;
};
// Two glboal variables to store address of front and rear nodes.
struct Node* front = NULL;
struct Node* rear = NULL;
// To Enqueue an integer
void Enqueue(struct cake x) {
struct Node* temp =
(struct Node*)malloc(sizeof(struct Node));
temp->cake = x;
temp->next = NULL;
if (front == NULL && rear == NULL){
front = rear = temp;
return;
}
rear->next = temp;
rear = temp;
}
// To Dequeue an integer.
void Dequeue() {
struct Node* temp = front;
if (front == NULL) {
printf("Queue is Empty\n");
return;
}
if (front == rear) {
front = rear = NULL;
}
else {
front = front->next;
}
free(temp);
}
struct cake Front() {
if (front == NULL) {
printf("Queue is empty\n");
return;
}
return front->cake;
}
void Print() {
struct Node* temp = front;
while (temp != NULL) {
printf("%d ", temp->cake.name);
temp = temp->next;
}
printf("\n");
}
int main(void){
Enqueue(redVelvet());
Enqueue(redVelvet());
Print();
getchar();
}
So In reality I'm going to have many different cakes, and if certain conditions are meant they are going to be inputted into the queue of LinkedList. However as a sample I created one type of cake (Red Velvet) And added it into the queue via my enqueue function and then tried to print it, However my out put is "88 88"
I want it to print the name of the Cake instead.
Following 2 line of code change needed
c.name = 'R';
Inside print function formatter type should match the type of variable
printf("%c ", temp->cake.name);
Well, i have a code that inserts a new struct in a list in alphabetically order but i'm with a little problem. I just can make it work has a function and when i call i make head = Insert(frota* head, char name). The code is the fallowing
typedef struct robot {
int bateria;
char nome[3];
int pos_x;
int pos_y;
int target_x;
int target_y;
int limpos;
int percorridos;
struct robot * next;
}frota;
frota* Insert(frota* head, char name){
frota* temp = (frota*)malloc(sizeof(frota));
if(temp == NULL){
printf("Unable to allocate memory for new node\n");
exit(-1);
}
temp->nome[0] = 'R';
temp->nome[1] = name;
int* prevtemp = head;
int* nexttemp = head;
if(head != NULL)
{
// Corner Case: First on the list
if(temp->nome[1] <= prevtemp->nome[1])
{
head = temp;
temp->next = prevtemp;
}
else
{
// CASE: Somewhere between the first and the list
while(nexttemp->next != NULL)
{
nexttemp = nexttemp->next;
if(temp->nome[1] >= prevtemp->nome[1] && temp->nome[1] <= nexttemp->nome[1])
{
prevtemp->next = temp;
temp->next = nexttemp;
break;
}
prevtemp = prevtemp->next;
}
// Corner Case: end of list
if(nexttemp->next == NULL)
{
nexttemp->next = temp;
}
}
}
else
{
// Corner Case: We had an empty list
head = temp;
}
}
My question is how to make the code to work and changing the value directly of the value head, making this way this function a procedure. The code that i tried is this:
void Insert(frota* head, char name){
frota* temp = (frota*)malloc(sizeof(frota));
if(temp == NULL){
printf("Unable to allocate memory for new node\n");
exit(-1);
}
temp->nome[0] = 'R';
temp->nome[1] = name;
int* prevtemp = *head;
int* nexttemp = *head;
if(*head != NULL)
{
// Corner Case: First on the list
if(temp->nome[1] <= prevtemp->nome[1])
{
*head = temp;
temp->next = prevtemp;
}
else
{
// CASE: Somewhere between the first and the list
while(nexttemp->next != NULL)
{
nexttemp = nexttemp->next;
if(temp->nome[1] >= prevtemp->nome[1] && temp->nome[1] <= nexttemp->nome[1])
{
prevtemp->next = temp;
temp->next = nexttemp;
break;
}
prevtemp = prevtemp->next;
}
// Corner Case: end of list
if(nexttemp->next == NULL)
{
nexttemp->next = temp;
}
}
}
else
{
// Corner Case: We had an empty list
*head = temp;
(*head)->next = NULL;
}
}
This way i cal the procedure as Insert(&head,name). Any help would be appreciate. When i run the code it appears segmentation fault and is not na memory error
PS: The code isn't entirely my responsible, found some part online....
Grateful
For starters:
Change
int* prevtemp;
to be
struct robot * prevtemp;
(same for nexttemp)
Change all
head
to
(*head)
Change all
frota
to
struct robot