How can I change the pointer named "* FIRST" that points on the first element of a linked list if I want to delete it's first element?
-my problem is that when I delete the first node, the pointer point in the seconde node.But when I display the adress of the element I pointed on, I found that FIRST=NULL.
Thank you in advance.
#include <stdio.h>
#include <stdlib.h>
typedef struct
{int note;
struct personne *next;
}personne;
personne *first=NULL;
void saisi (personne *first,int mark)
{ personne *nouveau=malloc(sizeof(personne));
nouveau->note=mark;
nouveau->next=NULL;
if(first==NULL)
first=nouveau; // here is the problem
else
{ personne *tmp;
tmp=first;
while (tmp->next!=NULL) tmp=tmp->next;
tmp->next=nouveau;
}
}
void affichage (personne *first)
{int i=1;
personne *tmp;
tmp=first;
do
{printf("la note %d : %d \n",i,tmp->note);
i++;tmp=tmp->next;
}while (tmp!=NULL);
}
void suppresion (personne *first,int n)
{personne *tmp1=NULL,*tmp2=NULL;
tmp1=first;
while (tmp1 != NULL)
{ if ((tmp1->note) >n){
tmp2->next=tmp1->next;
}
tmp2=tmp1;
tmp1=tmp1->next;
}
}
int main()
{
int N=1,mark=0,n=0;
while (N!=4)
{ printf ("donner la note %d:",N);
scanf ("%d",&mark);
saisi (first,mark);
N++;
}
affichage (first);
printf("donner n :");
scanf("%d",&n);
suppresion (first,n);
affichage(first);
return 0;
}
As commented by dasblinkenlight, use a pointer to pointer:
void saisi (personne **ppfirst, int mark)
{
personne **ppnode = ppfirst;
personne *nouveau=malloc(sizeof(personne));
nouveau->note=mark;
nouveau->next=NULL;
while(*ppnode != NULL)
ppnode = &((*ppnode)->next);
*ppnode = nouveau;
}
void suppresion (personne **ppfirst, int n)
{
personne **ppnode = ppfirst;
personne *pnode;
while (*ppnode != NULL)
{
if((*ppnode)->note > n){
pnode = *ppnode;
*ppnode = (*ppnode)->next;
free(pnode);
} else {
ppnode = &((*ppnode)->next);
}
}
}
/* ... */
saisi(&first, mark);
/* ... */
suppresion(&first, n);
1.- Since "first" is a global variable, you don't need to pass it as argument at each function call.
2.- At the "suppresion" method, "temp2" could be pointing to NULL when you try to call "temp2->next".
3.- You must free memory when deleting an element of your list.
4.- I don't understand well what are you asking, but if you want to delete many elements of your linked list, here is the way i would make the supression method, supposing that the method deletes all the nodes with a (mark > n):
void suppresion (int n)
{
personne *tmp1=NULL,*tmp2=NULL;
tmp1=first;
//First check all elements except the first one
while (tmp1 != NULL)
{
if ((tmp1->next != NULL)&&(tmp1->next->note >n))
{
tmp2=tmp1->next;
tmp1->next = tmp2->next;
free(tmp2);
}
else
{
tmp1=tmp1->next;
}
}
//Now go for the first element
if(first != NULL && first->note > n)
{
tmp1 = first;
first = tmp1->next;
free(tmp1);
}
}
That method searches all the elements of the array and delete all the elements that have a mark > n in just one method call; normally you create a method that deletes a concrete element and call it from a loop in another section of your code.
Related
My goal is to create a linked list and store elements inside that list.
struct node
{
int a;
struct node *b;
} p,*temp,*head;
void create ( struct node *temp)
{
char c;
temp = malloc (sizeof(struct node));
printf("enter data\n");
scanf(" %d",&temp->a);
printf("do you want to insert another node y/n\n");
scanf("%s", &c);
if (c=='y')
{
create(temp->b);
}
else if ( c=='n')
{
temp->b= NULL;
temp=&p;
return;
}
}
void traverse ( struct node *head)
{
while(head != NULL)
{
printf("%d ",head->a);
head=head->b;
}
}
int main ()
{
int i,j,k,l,m,n;
do{
if(i==1)
{
printf("enter data\n");
scanf("%d",&p.a);
create (p.b);
}
else if ( i==2)
traverse(temp);
}
while(i!=3);
printf("%d",temp->a);
}
I can't recover the elements once i've stored them. When I try to traverse the list, it only gives me the first element of the list and nothing else.
In main
do {
if(i==1)
{
...
}
else if ( i==2)
traverse(temp);
}
while(i!=3);
must be something like
do {
if (scanf("%d", &i) != 1)
break;
if(i==1)
{
...
}
else if ( i==2)
traverse(temp);
}
while(i!=3);
to know what the user want (i not initialized in your code)
in create
scanf("%s", &c);
is wrong because c is a char rather than a string
Do not mix read of int and char because you will read newline and space when reading a character, so read a string for c, for instance
char c[2];
...
scanf("%1s", &c);
if (*c == 'y')
...
else if (c == 'n')
...
the return in else branch is useless, and in case the answer is not 'y' or 'n' you do nothing so you do not set temps, probably you have to just check if 'y' and all other answers must be considered to be 'n', or you need to ask again for the choice
in create you assign the local variable temps, that has no effect on p.b in main, you need to get a node** for instance
in main temp is used but never set elsewhere, and the variables j,k,l,m,n are useless. You also ask for the data in main while you also do in create, must not be done in main. The way you manage your variables do not allow you to modify/print the list
I encourage you to not use global variables the must you can, and to not use the same name for a global and local variable like you do for temp and head because that do not help the reader of your code
A proposal solving the problems :
#include <stdlib.h>
#include <stdio.h>
struct node
{
int a;
struct node * b;
};
/* flush input up to the end of the line */
void flush()
{
int c;
while ((c = getchar()) != '\n') {
if (c == EOF)
exit(-1);
}
}
void create (struct node ** l)
{
/* go to the end of the list */
while (*l != NULL)
l = &(*l)->b;
for (;;) {
char c[2];
int v;
printf("enter data\n");
if (scanf("%d", &v) != 1) {
puts("invalid value");
flush();
}
else {
*l = malloc (sizeof(struct node));
(*l)->a = v;
(*l)->b = NULL;
l = &(*l)->b;
for (;;) {
printf("do you want to insert another node y/n\n");
scanf("%1s", c);
if (*c == 'y')
break;
else if (*c == 'n')
return;
}
}
}
}
void traverse ( struct node *head)
{
while(head != NULL)
{
printf("%d ",head->a);
head = head->b;
}
putchar('\n');
}
int main ()
{
int i;
struct node *head = NULL;
for (;;) {
puts("enter choice : 1 to create new node, 2 to print list, 3 to exit");
if (scanf("%d", &i) != 1)
flush();
switch(i) {
case 1:
create(&head);
break;
case 2:
traverse(head);
break;
case 3:
return 0;
default:
break;
}
}
}
Compilation and execution :
/tmp % gcc -pedantic -Wextra -Wall t.c
/tmp % ./a.out
enter choice : 1 to create new node, 2 to print list, 3 to exit
2
enter choice : 1 to create new node, 2 to print list, 3 to exit
1
enter data
11
do you want to insert another node y/n
y
enter data
22
do you want to insert another node y/n
n
enter choice : 1 to create new node, 2 to print list, 3 to exit
2
11 22
enter choice : 1 to create new node, 2 to print list, 3 to exit
1
enter data
3
do you want to insert another node y/n
n
enter choice : 1 to create new node, 2 to print list, 3 to exit
2
11 22 3
enter choice : 1 to create new node, 2 to print list, 3 to exit
4
enter choice : 1 to create new node, 2 to print list, 3 to exit
3
I encourage you to add the free of the list
There are several issues here:
struct node
{
int a;
struct node *b;
} p,*temp,*head;
Why do you declare global variables and use it as function parameters ? Global variables are available globally, there is no need to pass them into functions. On the other hand, global variables should be avoided and used with care, so it would be better to create local variables (e.g. in main function) and pass them as parameters into next functions.
void create ( struct node *temp)
{
char c;
temp = malloc (sizeof(struct node));
printf("enter data\n");
scanf(" %d",&temp->a);
printf("do you want to insert another node y/n\n");
scanf("%s", &c);
if (c=='y')
{
create(temp->b);
}
else if ( c=='n')
{
temp->b= NULL;
temp=&p;
return;
}
}
This function looks wrong. temp function parameter is actually an internal function's variable, that is not an in/out parameter. In that case you can assign to the temp variable, but it will not for a list. Also temp function parameter shadows temp global variable. It is also a good think to return status of operation, usually '0' means no error, any other error value.
Another thing is to keep things as simple as possible. This will allow for more reuseability and goes with single responsibility principle. If function actually performs two tasks it should be split into two functions.
One more thing, you allocate memory dynamically but never free the memory. This will lead into memory losses.
A possible implementation of your list could be:
#include <stdio.h>
#include <stdlib.h>
typedef struct _node_t
{
int a;
struct _node_t * next;
} node_t;
static node_t * head = NULL;
static node_t * tail = NULL;
node_t * create(void)
{
node_t * temp = malloc(sizeof(node_t));
if (NULL == temp)
{
return NULL;
}
printf("Enter data\n");
scanf("%d", & temp->a);
return temp;
}
void append(node_t * data)
{
if (NULL == head)
{
head = tail = data;
}
else
{
tail->next = data;
tail = tail->next;
}
tail->next = NULL;
return;
}
int add_data(void)
{
node_t * data = NULL;
char answer = 'y';
data = create();
if (NULL == data)
{
return 1;
}
append(data);
return 0;
}
void traverse(void)
{
node_t * current = NULL;
for (current = head; current != NULL; current = current->next)
{
printf("%d ", current->a);
}
printf("\n");
return;
}
void cleanup(void)
{
node_t * current = head;
while (NULL != current)
{
head = head->next;
free(current);
current = head;
}
return;
}
int main(int argc, char ** argv)
{
int option = 3;
do
{
printf("Enter option:\n 1 - add data\n 2 - traverse list\n 3 - exit\n\n");
scanf("%i", & option);
switch (option)
{
case 1:
if (0 != add_data())
{
printf("ERROR:: Cannot allocate memory.\n");
cleanup();
return 1;
}
break;
case 2:
traverse();
break;
default:
if (option > 3)
{
printf("ERROR:: Improper option, try again.\n");
}
break;
}
}
while (option != 3);
cleanup();
return 0;
}
I tried making it as simple as possible and keeping your logic there.
#include <stdio.h>
#include <stdlib.h>
struct node
{
int data;
struct node *next;
};
// create a new node
struct node* create(int data)
{
struct node *n = malloc(sizeof(struct node));
n->data = data;
n->next = NULL; // by default its not NULL, so we must set it
return n;
}
void traverse(struct node *head)
{
struct node *tmp = head;
while(tmp != NULL)
{
printf("%d\t",tmp->data);
tmp = tmp->next;
}
}
void cleanup(struct node *head)
{
struct node *cur = head;
struct node *next;
while(cur != NULL)
{
next = cur->next;
free(cur);
cur = next;
}
}
int main ()
{
int data;
struct node *head, *tmp;
// head node is always created
printf("enter data\n");
scanf("%d",&data);
head = tmp = create(data);
if(head == NULL) return -1;
// now we loop until we don't want to create any more nodes
while(1)
{
char another;
printf("do you want to insert another node y/n\n");
scanf(" %c", &another); // ignore all the previous whitespace
if(another == 'y')
{
printf("enter data\n");
scanf("%d",&data);
tmp->next = create(data);
tmp = tmp->next;
}
else break;
/*
// anything but 'y' breaks the loop, but it can be set to continue if neither 'y' nor 'n' was read:
else if(another == 'n') break;
else continue;
*/
}
traverse(head);
cleanup(head);
}
EDIT: as #Diodacus stated, i added cleanup and checking if malloc returned NULL
I'm trying to write a program that enqueue, dequeue, delete a chosen number and print the list. I have problems with the dequeue that i think is because of the menu part when you write a number, I've tried to fix it but the it removes the last number and not the first. The print shows the wrong number and when I tried to solve that problem I got the same problem as I had in dequeue. It's sometinhg wrong in delete but i cant figure it out.
I appreciate all the help i can get
edit:
I've changed it a lot and now everything else works except delete. I want delete to find the number i enter and delete it.
queue.c
#include <stdio.h>
#include <stdlib.h>
#include<conio.h>
struct node
{
int info;
struct node *ptr;
int next;
}*first, *last, *temp, *first1;
void enq(int data);
void deq();
void empty();
void display();
void create();
void delete_queue();
int count = 0;
void main()
{
int no, ch;
printf("\n 1 - Enqueue");
printf("\n 2 - Dequeue");
printf("\n 3 - Delete");
printf("\n 4 - Display");
printf("\n 5 - Exit");
create();
while (1)
{
printf("\n Enter choice : ");
scanf_s("%d", &ch);
switch (ch)
{
case 1:
printf("Enter data : ");
scanf_s("%d", &no);
enq(no);
break;
case 2:
deq();
break;
case 3:
printf("Enter data : ");
scanf_s("%d", &no);
delete_queue(no);
case 4:
display();
break;
case 5:
exit(0);
default:
printf("Wrong choice, Please enter correct choice ");
break;
}
}
}
void create()
{
first = last = NULL;
}
void enq(int data)
{
if (last == NULL)
{
last = (struct node *)malloc(1 * sizeof(struct node));
last->ptr = NULL;
last->info = data;
first = last;
}
else
{
temp = (struct node *)malloc(1 * sizeof(struct node));
last->ptr = temp;
temp->info = data;
temp->ptr = NULL;
last = temp;
}
count++;
}
void display()
{
first1 = first;
if ((first1 == NULL) && (last == NULL))
{
printf("Queue is empty");
return;
}
while (first1 != last)
{
printf("%d ", first1->info);
first1 = first1->ptr;
}
if (first1 == last)
printf("%d", first1->info);
}
void deq()
{
first1 = first;
if (first1 == NULL)
{
printf("\n Error: Trying to display elements from empty queue");
return;
}
else
if (first1->ptr != NULL)
{
first1 = first1->ptr;
printf("\n Dequed value : %d", first->info);
free(first);
first = first1;
}
else
{
printf("\n Dequed value : %d", first->info);
free(first);
first = NULL;
last = NULL;
}
count--;
}
void delete_queue()
{
int retval = -1;
if (first)
{
struct node *temp = first;
first = first->next;
if (!first) { last = first; }
retval = temp->next;
free(temp);
}
return retval;
}
void empty()
{
if ((first == NULL) && (last == NULL))
printf("\n Queue empty");
else
printf("Queue not empty");
}
Let me start with a few points of advice about design and style:
I do not recommend this:
typedef struct node {
int data;
struct node *next;
} node;
you are typedefing struct node to node. while it is not illegal, it is confusing. I would recommend
typedef struct _node {
int data;
struct _node *next;
} node;
Additionally, I do not recommend use of global variable with static storage class to keep track of your queue, instead you should create a queue in your main. Use global variables only when you have compelling reasons to do so.
Do remember that when you get rid of your global variable, you will need to rewrite your enqueue dequeue delete etc... functions to take in a queue_c * as parameter (because it wont have access to queueref any more)
Now for the reason that your code is not working properly and #Weather Vane alluded to:
you have a big problem in your delete function.
int delete(int data)
{
int result = 0;
node *curr_ptr; //pointer just created and not initialized
node *prev_ptr; //not initialized
node *temp_ptr; //not initialized
while (curr_ptr != NULL)
//curr_ptr was just created, where is it pointing? fatal error here
{
//inside this block lets imagine curr_ptr is pointing to a valid
//node in the global queue
if (curr_ptr->data == data)
{
result = 1;
if (curr_ptr->next != NULL)
{
temp_ptr = curr_ptr;
//both pointers point to the same thing
destroy_node(temp_ptr);
//now you just destroyed both nodes
prev_ptr->next = curr_ptr->next;
//the first time this block runs prev_ptr is uninitialized
//so prev_ptr->next will most likely seg fault
//this happens for example if you call this function
//for the first time with a long queue
}
else
{
temp_ptr = curr_ptr;
queueref.last = prev_ptr;
prev_ptr->next = NULL;
destroy_node(temp_ptr);
//again you are destroying both curr_ptr and temp_ptr
}
}
curr_ptr = curr_ptr->next;
prev_ptr = prev_ptr->next;
return result;
}
}
Perhaps it would be better if you think edge cases very carefully and rethink some of the logic from scratch. (test edge cases as you go)
I am trying to make a students list for a project in c
the functions inside the program are 3
insert = inserts students to the list
print = prints out the students available
delete = deletes a student from the list
I have created the program and it works fine using all three functions
and now I would like to make the same list using recursion.
I have made the print function recursive and it is working
now I am trying to make the delete function work the same way
unfortunately I am failing to make it work
In the code below if you run it you will see that it works only if you do not attempt to delete the last node on the list and if you do not tell it to delete a node that it does not exists.
#include <stdio.h>
#include <stdlib.h>
typedef struct tf *tp;
struct tf{
int am;
double gr;
tp next;
};
tp head, tail, temp, aux;
void insert1 (tp *h, tp t);
void print1(tp h);
void delete1(tp *h,int da);
int main()
{
char fry, fry2;
int am;
fry = 'a';
head = NULL;
tail = NULL;
while (fry != 'q')
{
printf("\n character given is %c\n", fry);
if (fry != 'q')
{
printf("new choice\n");
fry = 'a';
fflush(stdin);
fry = getchar();
getchar();
if (fry == 'q')
printf("quit\n");
if (fry == 'i')
{
fry2 = fry;
printf(" insert new student number am\n");
insert1(&head,tail);
fry = fry2;
}
if (fry == 'd')
{printf(" delete \n");
printf(" am number of student to be deleted\n");
scanf("%d", &am);
delete1(&head,am);
}
if (fry == 'p')
{
printf("\n printing\n");
print1(head);
}
}
}
}
void insert1 (tp *h, tp t)
{
tp te, a;
int da;
te = (tp)malloc(sizeof(struct tf));
printf(" am number for the new insert\n");
scanf("%d", &da);
getchar();
te->am = da;
te->next = NULL;
printf("am number is %d",te->am);
if ((*h != NULL) && (te->am < (*h)->am))
{
te->next = *h;
*h = te;
}
if((*h != NULL) && ((*h)->next != NULL) && (te->am > (*h)->am))
{
a=*h;
while((a->next != NULL) && (a->next->am < te->am))
{
a= a->next;
}
te->next = a->next;
a->next = te;
}
if((*h != NULL) && ((*h)->next == NULL) && (te->am > (*h)->am))
{
(*h)->next = te;
}
if(*h == NULL)
{
printf("\n head is null");
*h = te;
t = te;
}
}
void print1(tp h)
{
tp a;
a=h;
if (a==NULL)
return;
printf("%d\n",a->am);
print1(a->next);
}
void delete1(tp *h,int da)
{
tp a= *h,t= *h,temp = NULL;
if ((*h) != NULL)
{
if ((*h)->am!=da)
{
if (a->next->am != da && a->next!=NULL)
{
delete1(a->next,da);
}
else
{
if (a->next==NULL)
{
printf("am not found\n");
return;
}
else
{
temp = a->next;
a->next = a->next->next;
free(temp);
}
}
}
else
{
a = (*h);
(*h)= (*h)->next;
free(a);
}
}
else
{
printf("empty list");
}
}
As you can see I want the delete function to delete the node by looking for the am number given,so it will first search the list to find if the am number is there or not.
If anyone can give me a tip on how to make the delete function to work I would be grateful.
There are several things going on. This line:
if (a->next->am != da && a->next!=NULL) ...
should have the conditions swapped, otherwise you might access a->next withot verifying that it isn't NULL first. The auxiliary variable a and the other temporaries are confusing rather than helpful.
You pass the head to the delete1 function as pointer to pointer, so that the head can be updated. But this doesn't affect only the head: This adds a level of indirection thoughout your iteration.
For your iterative calls, this means that you must pass the address of the pointer that stores the reference to the current node, (*h)->next. At the beginning, this is the address of the head. On subsequent iterations, this is the address of the next pointer of the previous node.
There's also no need to consider various cases. The code can be as simple as:
void delete1(tp *h, int da)
{
if (*h != NULL) {
if ((*h)->am == da) {
tp next = (*h)->next;
free(*h);
*h = next;
return;
}
delete1(&(*h)->next, da);
}
}
The recursive call happens at the end of the function or it doesn't happen at all. This means that you can rewrite the code as a loop:
void delete1(tp *h, int da)
{
while (*h != NULL) {
if ((*h)->am == da) {
tp next = (*h)->next;
free(*h);
*h = next;
return;
}
h = &(*h)->next;
}
}
This will save you some stack space on large lists. Your insert1 function could also be cleaned up and simplified.
My list :
list= C,3 -->C,5,---> A,7 --> A,5 --> G,2--> C,11 -->A,4
my outuput :
output= C,5 C,11 G,2 A,7 A,4 A,5 C,3
but there is some mistakes. I write my code like in answers and I write charcmp function and replace with strcmp with charcmp. It works sometime corrcectly. But usually first element is in the wrong place .My sorting code likes answer's code
try this:-
#include<stdio.h>
#include<stdlib.h>
/*Queue has five properties. capacity stands for the maximum number of elements Queue can hold.
Size stands for the current size of the Queue and elements is the array of elements. front is the
index of first element (the index at which we remove the element) and rear is the index of last element
(the index at which we insert the element) */
typedef struct Queue
{
int capacity;
int size;
int front;
int rear;
int *elements;
}Queue;
/* crateQueue function takes argument the maximum number of elements the Queue can hold, creates
a Queue according to it and returns a pointer to the Queue. */
Queue * createQueue(int maxElements)
{
/* Create a Queue */
Queue *Q;
Q = (Queue *)malloc(sizeof(Queue));
/* Initialise its properties */
Q->elements = (int *)malloc(sizeof(int)*maxElements);
Q->size = 0;
Q->capacity = maxElements;
Q->front = 0;
Q->rear = -1;
/* Return the pointer */
return Q;
}
void Dequeue(Queue *Q)
{
/* If Queue size is zero then it is empty. So we cannot pop */
if(Q->size==0)
{
printf("Queue is Empty\n");
return;
}
/* Removing an element is equivalent to incrementing index of front by one */
else
{
Q->size--;
Q->front++;
/* As we fill elements in circular fashion */
if(Q->front==Q->capacity)
{
Q->front=0;
}
}
return;
}
int front(Queue *Q)
{
if(Q->size==0)
{
printf("Queue is Empty\n");
exit(0);
}
/* Return the element which is at the front*/
return Q->elements[Q->front];
}
void Enqueue(Queue *Q,int element)
{
/* If the Queue is full, we cannot push an element into it as there is no space for it.*/
if(Q->size == Q->capacity)
{
printf("Queue is Full\n");
}
else
{
Q->size++;
Q->rear = Q->rear + 1;
/* As we fill the queue in circular fashion */
if(Q->rear == Q->capacity)
{
Q->rear = 0;
}
/* Insert the element in its rear side */
Q->elements[Q->rear] = element;
}
return;
}
int main()
{
Queue *Q = createQueue(5);
Enqueue(Q,1);
Enqueue(Q,2);
Enqueue(Q,3);
Enqueue(Q,4);
printf("Front element is %d\n",front(Q));
Enqueue(Q,5);
Dequeue(Q);
Enqueue(Q,6);
printf("Front element is %d\n",front(Q));
}
The following code should do the work. It will add to the list in increasing age order:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct _node_t {
int age;
char *name;
struct _node_t *nextPtr;
} node_t;
node_t *node;
void enqueue(char *name, int age)
{
node_t *p, *prev, *n;
/* if empty list create first element and return */
if (node == NULL)
{
node = (node_t *)malloc(sizeof(node_t));
node->nextPtr = NULL;
node->name = (char *)malloc(strlen(name) + 1);
strcpy(node->name, name);
node->age = age;
return;
}
p = prev = node;
/* search last element or element with superior age value */
while((p->nextPtr != NULL) && strcmp(p->name, name) < 0)
{
prev = p;
p = p->nextPtr;
}
if (strcmp(p->name, name) == 0)
{
while((p->nextPtr != NULL) && p->age < age)
{
prev = p;
p = p->nextPtr;
}
}
/* create the new element and store the data */
n = (node_t *)malloc(sizeof(node_t));
n->name = (char *)malloc(strlen(name) + 1);
strcpy(n->name, name);
n->age = age;
/* insert the new element */
if ((strcmp(p->name, name) < 0) || (strcmp(p->name, name) == 0 && p->age < age))
{
n->nextPtr = p->nextPtr;
p->nextPtr = n;
}
else
{
n->nextPtr = p;
if (prev->nextPtr == p)
{
prev->nextPtr = n;
}
else if (node == p)
{
node = n;
}
}
}
void printNodes()
{
node_t *p;
p = node;
while(p != NULL)
{
printf("%s, %d\n", p->name, p->age);
p = p->nextPtr;
}
}
int main(int argc, char **argv)
{
node = NULL;
enqueue("Kill", 15);
enqueue("Bill", 2);
enqueue("Kill", 7);
printNodes();
return 0;
}
So the following adding:
enqueue("Kill", 15);
enqueue("Bill", 2);
enqueue("Kill", 7);
Will store it in the order printed by printNodes():
Bill, 2
Kill, 7
Kill, 15
UPDATED:
Added name sorting then age.
A solution using double pointers is probably the best. You are implementing a priority queue technically, not a list. You implement it by keeping a linked list that is sorted. The dequeue operation on a priority queue will remove the first item from the list.
As this is a homework assignment I set it up for you but you need to complete the rest so you can actually learn the important stuff.
EXIT CONDITION HERE -> This is where you want to check when you have found the item where you will insert after. Write this condition so that the loop exits when this occurs.
EDIT ^^ -> When I say the item where you will insert after what I mean is that the item you currently are looking at is the first item that is "greater" than temp. queue will be pointing to the next pointer to that item. I also added a line in the code that will make set temp's next to point to that item. When you update *queue you are saying that you want to make the next pointer on the previous item point to *temp.
update the pointer here -> This is where you update queue to point to the next pointer of the next person in the list/queue.
typedef struct Person {
char name[20];
int age;
struct Person *next;
} Person;
void enqueue(Person **queue, char *name, int age) {
Person *temp = calloc(1, sizeof(Person));
strncpy(temp->name, name, 20);
temp->age = age;
while (*queue && "EXIT CONDITION HERE")
//update the pointer here;
temp->next = *queue; //forgot this line originally. You need it!!
*queue = temp; //.this sets the next pointer of last item or head to temp
}
...
Person *queue = NULL;
enqueue(&queue, "Bob", 10);
enqueue(&queue, "John", 5);
Then print the list to check that enqueue works correctly.
I need to sort the numbers that are entered in a list, but I am doing something wrong and it's sorting all of them except the first one.Any ideas how to fix this?
Here's my code:
#include <stdio.h>
#include <stdlib.h>
struct node
{
int data;
struct node *next;
};
struct node* List;
void Add (struct node* p, int d)
{
struct node* q;
q=malloc(sizeof(struct node));
if (q==NULL)
printf("Not enaugh memory!");
else
{
q->data=d;
if(List==NULL)
{
q->next=NULL;
List=q;
}
else
{
struct node *ptr=List;
while((ptr->next!=NULL)&&(ptr->next->data>d))
{
ptr=ptr->next;
}
q->next=ptr->next;
ptr->next=q;
}
}
}
int main()
{
int n,i,a;
printf("How much numbers are you going to enter? ");
scanf("%d",&n);
for (i=1; i<=n; i++)
{
printf("\nEnter a number: ");
scanf("%d",&a);
Add(List,a);
}
printf("\nThe sorted numbers are: ");
struct node *ptr=List;
while(ptr!=NULL)
{
printf("%d\t",ptr->data);
ptr=ptr->next;
}
printf("\n\n");
system("PAUSE");
return 0;
}
Thanks for the help in advance :-)
in add() function,
if(List==p)
this statement is true for all elements you insert to list since the call to add is,
Add(List,a);
so p=List. therefore the sorting code written in else part is not executed.
Also add statements to check for empty initial list.
You can use code similar to this,
void Add (int d)
{
struct node* q;
q=malloc(sizeof(struct node));
if (q==NULL)
printf("Not enaugh memory!");
else
{
q->data=d;
if(List==NULL)
{
q->next=NULL;
List=q;
}
else
{
struct node *ptr=List;
while((ptr->next!=NULL)&&(ptr->next->data>d))
{
ptr=ptr->next;
}
q->next=ptr->next;
ptr->next=q;
}
}
}
Since list is a global variable you dont need to pass it to Add() function. change the function call to
Add(a);
void Add (struct node* p, int d){
struct node* q;
q=malloc(sizeof(struct node));
if (q==NULL)
printf("Not enaugh memory!");
else{
q->data=d;
if(List==NULL || List->data < d){//modify this line
q->next= List;//and change NULL to List
List=q;
} else {
struct node *ptr=List;
while((ptr->next!=NULL)&&(ptr->next->data>d)){
ptr=ptr->next;
}
q->next=ptr->next;
ptr->next=q;
}
}
}
You always call Add with List as the first parameter, so it's alway true inside Add that (List==p). Consequently each new item is just inserted at the front of the list and there is no sorting at all.
EDIT 1
A good practice would be sending a list to the Add routine as a parameter. Or, if you want to keep it external, just don't give it to Add at all and test if(List == NULL)
void Add( int d)
{
// ... alloc 'q' and fill q->d here, then:
if(List == NULL)
{
q->next = NULL;
List = q;
}
else
{
struct node *b; // put q after b
for( b = List; b->next != NULL; b = b->next)
if( b->next->data >= d)
break;
q->next = b->next;
b->next = q;
}
}
EDIT 2
Example of transferring the list to a function by parameter
void Add( struct node **n, int d)
{
// ... alloc 'q' and fill q->d here, then:
while( *n != NULL && (*n)->data < d)
n = & (*n)->next;
q->next = *n;
*n = q;
}
int main()
{
// ...
Add( &List, a);
// ...
}