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linked lists using dynamic memory allocation

Posted on 2000-04-29
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Last Modified: 2012-05-04
The purpose of this program is to create a linked list using dynamic memory allocation to store a person's id,firstname,surname and age.I have one error which is repeated several times throughout the list.c program. The error is ' assignment makes integer from pointer without cast'. I have no idea what this means.
One place that it occurs is in the search() function on the line:
for (p=l->head;p!=NULL;p=p->next).
It also occurs in my delete() and insert().
Can anyone give me any hints as to the problem?
I have written functions for initialise and print and these compile fine.

Structure definitions:
#define NAMESIZE 20

struct person
{
int id;
char firstname[NAMESIZE];
char surname[NAMESIZE];
int age;
};

struct item
{
int next;
struct person details;
};

struct list
{
int head;
int tail;
struct item *item;
};


Function prototypes:
struct item * search(struct list *l, int);
struct item * insert(struct list *l, struct person);
int delete(struct list *,int);


Functions:
struct item * search(struct list *l, int id)
{
struct item *p;
for(p=l->head;p=NULL;p=p->next)
        if(p->details.id==id)
        {
                break;
                return(p);
        }
        else
        {
                return(NULL);
        }
}

struct item * insert(struct list *l, struct person data)
{
struct item *item;
struct item *ptr;

item=(struct item*)malloc(sizeof(struct item)); /*get new item*/
item->details.id=data.id;                     /*assign data*/
strcpy(item->details.firstname,data.firstname);
strcpy(item->details.surname,data.surname);
item->details.age=data.age;                  
item->next=NULL;                                /*initialise next pointer*/

if(l->head==NULL)
        &l->head=item;
else
{
/*find list item in list which is the first one with a null pointer*/
        for(ptr=l->head;ptr->next=NULL;ptr=ptr->next)  /*this is a null statement*/
                ptr->next=item;
}
       

return (item);
}

int delete(struct list *l,int id)
{
struct item *temp;

if(search(l,id)!=NULL)   /*item found in list, continue deleting*/

{
        if(l->head==NULL)   /*delete the first item*/
        {
                temp=l->head;
                l->head=temp->next;
        }

        else
        {
                temp=temp->next;     /*delete the next item*/
                temp->next=temp->next;
        }
               

        free (temp);
        return(1);     /*return 1 to indicate successful delete*/
}
else   /*item not found, return 0 */
return(0);
       
}



0
Comment
Question by:Gizmo1
  • 2
3 Comments
 

Accepted Solution

by:
sa9813 earned 50 total points
ID: 2763320
I have commented in the code where the problems are, the ones you are reffering to in your question. Basically what you are trying to do is to assing an int (l->head) to a pointer of some kind. Maybe this gets you on the right track.

#define NAMESIZE 20

struct person {
      int id;
      char firstname[NAMESIZE];
      char surname[NAMESIZE];
      int age;
};

struct item {
      int next;
      struct person details;
};

struct list {
      int head;
      int tail;
      struct item *item;
};



struct item * search(struct list *l, int);
struct item * insert(struct list *l, struct person);
int delete(struct list *,int);



struct item * search(struct list *l, int id) {
struct item *p;

//p = l->head   p is a struct item pointer
//in your struct list head is an int. You are here
//assigning an int to a struct item pointer!

for(p=l->head;p=NULL;p=p->next)
        if(p->details.id==id)
        {
                break;
                return(p);
        }
        else
        {
                return(NULL);
        }
}


struct item * insert(struct list *l, struct person data) {
      struct item *item;
      struct item *ptr;

      item=(struct item*)malloc(sizeof(struct item)); /*get new item*/
      item->details.id=data.id;                     /*assign data*/
      strcpy(item->details.firstname,data.firstname);
      strcpy(item->details.surname,data.surname);
      item->details.age=data.age;                    
      item->next=NULL;                                /*initialise next pointer*/

      if(l->head==NULL)
        &l->head=item;
      else {

            //same thing goes here, you are trying to assign
            //a int to a struct item pointer
            //ptr = l->head!
        for(ptr=l->head;ptr->next=NULL;ptr=ptr->next)  
                ptr->next=item;
      }
      return (item);
}


int delete(struct list *l,int id)
{
struct item *temp;

if(search(l,id)!=NULL)   /*item found in list, continue deleting*/

{
        if(l->head==NULL)   /*delete the first item*/
        {

                        //same thing here, temp = l->head!

                temp=l->head;
                l->head=temp->next;
        }

        else
        {
                temp=temp->next;     /*delete the next item*/
                temp->next=temp->next;
        }
                 

        free (temp);
        return(1);     /*return 1 to indicate successful delete*/
}
else   /*item not found, return 0 */
return(0);
         
}





0
 

Author Comment

by:Gizmo1
ID: 2763401
I know what the problem is(trying to assign an int to a struct pointer) but how do I fix it?
Thanks.
0
 

Expert Comment

by:sa9813
ID: 2763456
I did not check the logic of you program, just for the errors you were asking about. But I think that you would want the head, next, tail to be pointers, used to navigate throug your structure. There is no logic having them as int's.
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