circular linked list question..

i need to go from the head of the linked list
and check if i got to the same place
after making circle.
the problem is if tell ptr=head;
and then the while condition checks if i didnt got to this place.
so it doesnt even enters this loop.

how to solve it

Code:

---

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct node node;
struct node{
        int value;
        struct node * next;
};

void main()
{
node* head;
head=(node*)malloc(sizeof(node));
        head->next=(node*)malloc(sizeof(node));
        head->next->next=(node*)malloc(sizeof(node));
        head->next->next->next=(node*)malloc(sizeof(node));
        head->next->next->next->next=(node*)malloc(sizeof(node));
        head->next->next->next->next->next=(node*)malloc(sizeof(node));
    head->next->next->next->next->next->next=head;
        head->value=2;
        head->next->value=4;
        head->next->next->value=1;
        head->next->next->next->value=5;
        head->next->next->next->next->value=3;
        head->next->next->next->next->next->value=8;

}

 int checkround(node *head)
 {
        int temp=head->value,n_temp;
        node * ptr;
        node * h_ptr


          ptr=head;//i need this in order to start going threw the list from this place
      while(ptr!=head)///have problem here
      {
          for(temp=n_temp;tem>0;temp=temp-1)
          {
                  ptr=ptr->next;
          }
          n_temp=ptr->value;
          ptr->value=-1;
      }

 }

---

Code:

---

while(ptr!=head)///have problem here {
    for(temp=n_temp;tem>0;temp=temp-1) {
        ptr=ptr->next;
    }

    n_temp=ptr->value;
    ptr->value=-1;
}

---

should really be a do-while loop. Or do one pass and then add the loop.

i cant understand why it doesnt skip 4 nodes
in the end of the first "for " loop it should point to
node 8
but it points to point 3
why??

Code:

---

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

typedef struct node node;
struct node{
        int value;
        struct node * next;
};
int checkround(node *head);
void main()
{
        int g;
node* head;
head=(node*)malloc(sizeof(node));
        head->next=(node*)malloc(sizeof(node));
        head->next->next=(node*)malloc(sizeof(node));
        head->next->next->next=(node*)malloc(sizeof(node));
        head->next->next->next->next=(node*)malloc(sizeof(node));
        head->next->next->next->next->next=(node*)malloc(sizeof(node));
    head->next->next->next->next->next->next=head;
        head->value=2;
        head->next->value=4;
        head->next->next->value=1;
        head->next->next->next->value=5;
        head->next->next->next->next->value=3;
        head->next->next->next->next->next->value=8;
g=checkround(head->next);
}

 int checkround(node *head)
 {
        int temp,n_temp;
        node * ptr;
 


          ptr=head;
      do
      {
          for(temp=ptr->value;temp>0;temp=temp-1)  \\here is the problem
          {
                  ptr=ptr->next;
          }
          n_temp=ptr->value;
                  if (n_temp==-1) return 0;
          ptr->value=-1;
      }while(ptr!=head);

        ptr=head;
                do
                {
          if (ptr->value!=-1)
                  {
            return 1;
                  }
                  ptr=ptr->next;
         
                }while(ptr!=head);
          return 2;

 }

---

i have written the for loop
so it will count from 4 to 1
and in each count it will go next on the list

so why it stops one step before the target

Code:

---

void main()

---

Did you forget that main returns an int?

Code:

---

head=(node*)malloc(sizeof(node));

---

FYI, the cast is unnecessary.

Code:

---

int checkround(node *head);

---

The name "checkaround" is misleading, since it actually alters the data structure. Try to use more meaningful names.

Code:

---

head=(node*)malloc(sizeof(node));
        head->next=(node*)malloc(sizeof(node));
        head->next->next=(node*)malloc(sizeof(node));
        head->next->next->next=(node*)malloc(sizeof(node));
        head->next->next->next->next=(node*)malloc(sizeof(node));
        head->next->next->next->next->next=(node*)malloc(sizeof(node));
    head->next->next->next->next->next->next=head;
        head->value=2;
        head->next->value=4;
        head->next->next->value=1;
        head->next->next->next->value=5;
        head->next->next->next->next->value=3;
        head->next->next->next->next->next->value=8;

---

Think modular. A simple function would make this so much easier. Consider something along these lines:

Code:

---

node * add_node(node **head, int value)
{
        node* ptr = (node*)malloc(sizeof(node));
        if(ptr == NULL)
                return NULL;
        if(*head == NULL)
                *head = ptr;       
        ptr->next = *head;
        ptr->value = value;       
        node *current = *head;
        while(current->next != *head)
                current = current->next;
        current->next = ptr;
        return ptr;       
}

---

Then, in main, you can simply do:

Code:

---

int main( void )
{
        node *head = NULL;
        add_node(&head, 2);
        add_node(&head, 4);
        add_node(&head, 1);
        add_node(&head, 5);
        add_node(&head, 3);
        add_node(&head, 8);
        return 0;
}

---

>> so why it stops one step before the target

Print the values of all of the variables involved as you go around the data structure.

Code:

---

void print_list(node *head)
{
        if(head == NULL)
                return;
        node *current = head;
        do
        {
                printf("%x: %d\n", current, current->value);
                current = current->next;
        }
        while(current != head);               
}

int checkround(node *head)
 {
        int temp,n_temp;
        node * ptr;
          ptr=head;
      do
      {
          printf("Begin Loop: ptr: %x, ptr->value: %d\n", ptr, ptr->value);     
          for(temp=ptr->value;temp>0;temp=temp-1)  //here is the problem
          {
                  printf("ptr: %x, ptr->value: %d, temp: %d\n", ptr, ptr->value, temp);
                  ptr=ptr->next;
          }
          n_temp=ptr->value;
                  if (n_temp==-1) return 0;
          ptr->value=-1;
      }while(ptr!=head);

        ptr=head;
                do
                {
          if (ptr->value!=-1)
                  {
            return 1;
                  }
                  ptr=ptr->next;
         
                }while(ptr!=head);
          return 2;

 }

int main( void )
{
        node *head = NULL;
        add_node(&head, 2);
        add_node(&head, 4);
        add_node(&head, 1);
        add_node(&head, 5);
        add_node(&head, 3);
        add_node(&head, 8);
        puts("List:");
        print_list(head);
        puts("Check:");
        checkround(head);
        return 0;
}

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Finally, I would recommend indenting your code consistently, and giving your variables more "room to breath" (eg: instead of "a==-1" use "a == -1").