Compiling error for linked list in c

Question

I did my whole project in NetBeans on my mac and it works fine. Then I go to put it into terminal to submit it on our ssh server for school and its giving me a bunch of compilation errors. Did netbeans compile in c++ or something? I'm new to c so any help is certainly appreciated. Here's the code.

/* 
 * File:   LinkedList.c
 * Author: dpiganell
 *
 * Created on October 17, 2011, 2:31 PM
 */

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

struct element{
    int i;
    struct element *next;
};

void insert(struct element**, struct element*);
void purge (struct element*, struct element*);
void printList(struct element*);
void printListBackwards(struct element*);

struct element *h;

int main() 
{
    // HEAD
    h = (element *) malloc(sizeof(element));
    h = NULL;

    // NEW VALUE
    struct element *n = NULL;

    // POINTER TO THE POINTER OF HEAD
    struct element **headPointer;
    headPointer = (element **) malloc(sizeof(element));

    int a;
    a = 1;
    while(a >= 0)
    {
        n = (element *) malloc(sizeof(element));

        printf("\nPlease enter an integer value: ");
        scanf("%d", &a);

        if(a >= 0)
        {
            n->i = a;
            n->next = NULL;
            headPointer = &h;

            insert(headPointer, n);

        n = n++;


      }
        printList(h);
        printListBackwards(h);
    }

    return 0;
}


void insert(struct element **head, struct element *n)
{
    element *nptr, *pptr, *cptr;
    // NEW POINTER, PREVIOUS POINTER, CURRENT POINTER

    nptr = (element *) malloc(sizeof(element));

    int purged;
    purged = -1;
    if(nptr != NULL)
    {
        nptr->i = n->i;
        nptr->next = NULL;

        cptr = *head;
        pptr = NULL;
    }

    while(cptr != NULL &&  n->i >= cptr->i)
    {
        if(cptr->i == n->i && purged != 1)
        {
            purged = 1;
            purge(cptr, pptr);
        }
        else
        {
            pptr = cptr;
            cptr = cptr->next;
        }
    }

    if(pptr == NULL && purged < 0)
    {
        nptr->next = *head;
        *head = nptr;
    }
    else if(purged < 0)
    {
        pptr->next = nptr;
        nptr->next = cptr;
    }
}


void purge(struct element *current, struct element *predecessor)
{
    element *ptr = (element *) malloc(sizeof(element));

    // ERASING THE HEAD
    if(predecessor == NULL)
    {
        if(current->next == NULL)
        {
            current->next = NULL;
            current->i = NULL;
            current = NULL;
            free(current);
            h = NULL;
        }
        else
             memcpy(current, current->next, sizeof(element));
    }

    // ERASING THE TAIL
    else if(current->next == NULL)
    {
        current->i = NULL;
        free(current->next);
        free(current);
        predecessor->next = NULL;
    }

    // ERASING ANYTHING IN THE MIDDLE OF THE LIST
    else
    {
        ptr = current->next; 
        predecessor->next = ptr;
        current->i = NULL;
        free(current->next);
    }
}

void printList(struct element *head)
{
    if(head == NULL)
        printf("The list is empty.");
    else
    {
        struct element *ptr;
        ptr = (element*) malloc(sizeof(element));    
        ptr = head;  

        int a;
        a = 1;
        printf("Forwards: ");
        while(a > 0)
        {
            printf("%d ", ptr->i);
            if((ptr->next) == NULL)
                a = -1;
            else
                ptr = ptr->next;

        }
    }
}

void printListBackwards(struct element *ptr)
{
    if(ptr == NULL)
    {
        // DO NOTHING BECAUSE IT WILL BE PRINTED ALREADY THAT IT IS EMPTIED
    }
    else
    {
        element *cptr = (element *) malloc(sizeof(element));
        cptr = ptr;
        if(ptr->next == NULL)
            printf("\nBackwards: %d ", ptr->i);
        else
        {
            printListBackwards(ptr->next);
            printf("%d ", ptr->i);
        }
    }
}

Also, here are the errors. It works fine and compiles fine in netbeans.

LinkedList.c:14: warning: useless keyword or type name in empty declaration
LinkedList.c: In function `main':
LinkedList.c:26: error: `element' undeclared (first use in this function)
LinkedList.c:26: error: (Each undeclared identifier is reported only once
LinkedList.c:26: error: for each function it appears in.)
LinkedList.c:26: error: syntax error before ')' token
LinkedList.c:34: error: syntax error before ')' token
LinkedList.c:40: error: syntax error before ')' token
LinkedList.c: In function `insert':
LinkedList.c:65: error: `element' undeclared (first use in this function)
LinkedList.c:65: error: `nptr' undeclared (first use in this function)
LinkedList.c:65: error: `pptr' undeclared (first use in this function)
LinkedList.c:65: error: `cptr' undeclared (first use in this function)
LinkedList.c:68: error: syntax error before ')' token
LinkedList.c: In function `purge':
LinkedList.c:110: error: `element' undeclared (first use in this function)
LinkedList.c:110: error: `ptr' undeclared (first use in this function)
LinkedList.c:110: error: syntax error before ')' token
LinkedList.c: In function `printList':
LinkedList.c:153: error: `element' undeclared (first use in this function)
LinkedList.c:153: error: syntax error before ')' token
LinkedList.c: In function `printListBackwards':
LinkedList.c:179: error: `element' undeclared (first use in this function)
LinkedList.c:179: error: `cptr' undeclared (first use in this function)
LinkedList.c:179: error: syntax error before ')' token

Are you sure you're showing us the exact code that gave you those errors? When I compile it, the first error I see is that element is undeclared (in C, that type's name is struct element). I can't reproduce the errors you're seeing in C++ either. — Keith Thompson
– Keith Thompson, Commented Oct 20, 2011 at 23:15
@KeithThompson The errors aren't in C++. The question was answered though thanks for the help. I compiled it in netbeans in a c++ compiler and it worked. But when I used gcc it didn't work just to clear things up. Thanks everyone. — Dominick Piganell
– Dominick Piganell, Commented Oct 20, 2011 at 23:18
Keith knows. But the program is supposed to be C, not c++. Also: you malloc() too much. — wildplasser
– wildplasser, Commented Oct 20, 2011 at 23:20

K-ballo · Accepted Answer · 2011-10-20 23:14:42Z

5

In C, this definition

struct element{
    int i;
    struct element *next;
};

has to be referred to as struct element. You get that right in some places, not all. A known idiom is:

typedef struct element { 
    int i;
    struct element *next;
} element;

Which typedefs element as struct element so you don't need to place struct in front of the type. This was so common that C++ kind of "does this for you" so struct is no longer needed.

answered Oct 20, 2011 at 23:14

K-ballo

81.6k20 gold badges165 silver badges172 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Karoly Horvath · Accepted Answer · 2011-10-20 23:13:42Z

4

It's C, you cannot use bare element, it's struct element.

answered Oct 20, 2011 at 23:13

Karoly Horvath

96.7k11 gold badges123 silver badges181 bronze badges

Comments

Nate · Accepted Answer · 2011-10-20 23:20:51Z

Your issues are related to how you declare your struct element vs. how you use it.

typedef struct element{
    int i;
    struct element *next;
} element;

will give you more satisfactory results.

Alternately, you can leave your struct as it is, wherever you use a bare element, instead write struct element.

BTW:

This isn't related to your exact problem, but I thought I would share (as my compiler gave me a warning about it); you sometimes write:

current->i = NULL;

In this case, i is an integer. In C, NULL is traditionally used only for pointer types. So as not to confuse, you should either change the assignment to:

current->i = 0;

...or, if i actually is meant to point to memory somewhere (which given the context above, I presume it is not), declare it as a pointer type.

Awais Qarni · Accepted Answer · 2011-10-21 05:33:53Z

1

You need to typedef your struct if you're going to use it that way. Otherwise you need to use the struct keyword everywhere. Check documentation

So you want to say:

typedef struct element {
   int i;
   element *next;
} element;

when you declare element. Otherwise the compiler doesn't know that element is a structure every time you use it.

edited Oct 21, 2011 at 5:33

Awais Qarni

18k25 gold badges80 silver badges145 bronze badges

answered Oct 20, 2011 at 23:20

mday299

1391 silver badge6 bronze badges

Comments

wildplasser · Accepted Answer · 2011-10-21 00:00:28Z

h = (element *) malloc(sizeof(element));
h = NULL;
headPointer = (element **) malloc(sizeof(element));

This is your first error. element is a struct tag, not a typedef. (this has been handled by the others.)

in the loop:

headPointer = &h;

Both pointers have been assigned (malloc()d) values. By re-assigning them, you lose the stuff what was previously malloc()d.

The 'headPointer' stuff is a good idea. It is a pointer that can point to other pointers. You can use it to let a called function alter the the value of on of the callers pointers. But your usage is not right. Normally the caller should do:

struct clown *pipo=NULL;
...
my_function( &pipo);

Inside the function, the caller's pointer can than be altered:

void my_function (struct clown **ppp) {
   ...
   *ppp = malloc (sizeof (struct clown));
   ...
 }

After the function returned, the caller can use the pointer, and it will hopefully point at the new clown. That's all.

Collectives™ on Stack Overflow

Compiling error for linked list in c

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

5 Answers 5

Comments

Comments

Comments

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related