• C

Some help with simple code

I have been given some simple code to get me used to using structs to create linked lists.
The code I was given is :

struct node {
      int data;
      struct node *next_ptr;
}

struct node *node_1, *node_2;

node_1 = malloc (sizeof(struct node));
node_2 = malloc (sizeof(struct node));

node_1->next_ptr=node2;


This creates 2 structs and sets one struct to point to the other, e.g creating the linked list.

So I tried to make a program to test out the code as follows

#include <stdio.h>





int main()
{

struct node {
      int data;
      struct node *next_ptr;
}


struct node *node_1, *node_2;

node_1 = malloc (sizeof(struct node));
node_2 = malloc (sizeof(struct node));

node_1->next_ptr=node2;

  return (0) ;
}


But when I compile i get
test.c: In function `main':
test.c:16: two or more data types in declaration of `node_1'
test.c:16: two or more data types in declaration of `node_2'
test.c:18: warning: assignment makes pointer from integer without a cast
test.c:19: warning: assignment makes pointer from integer without a cast
test.c:21: `node2' undeclared (first use in this function)
test.c:21: (Each undeclared identifier is reported only once
test.c:21: for each function it appears in.)

I cant see where Im going wrong as I used the exact test code I was given


welsh_boyAsked:
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DexstarCommented:
@welsh_boy:

> So I tried to make a program to test out the code as follows

Here are some corrections:
      #include <stdio.h>

      struct node {
            int data;
            struct node *next_ptr;
      };

      int main()
      {
            struct node *node_1, *node_2;

            node_1 = malloc (sizeof(struct node));
            node_2 = malloc (sizeof(struct node));

            node_1->next_ptr=node2;

            return (0) ;
      }

Hope That Helps,
Dex*
Gratch06Commented:
struct node {
    int data;
    struct node *next_ptr;
};   //missing a semicolon here.
welsh_boyAuthor Commented:
thanks for the quick reply Dex

I still get

gcc test.c -o test
test.c: In function `main':
test.c:12: warning: assignment makes pointer from integer without a cast
test.c:13: warning: assignment makes pointer from integer without a cast
test.c:15: `node2' undeclared (first use in this function)
test.c:15: (Each undeclared identifier is reported only once
test.c:15: for each function it appears in.)
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DexstarCommented:
@welsh_boy:

> I still get

More corrections:
Here are some corrections:
     #include <stdio.h>

     struct node {
          int data;
          struct node *next_ptr;
     };

     int main()
     {
          struct node *node_1, *node_2;

          node_1 = (struct node*)malloc (sizeof(struct node));
          node_2 = (struct node*)malloc (sizeof(struct node));

          node_1->next_ptr = node_2;

          return (0) ;
     }

Dex*
welsh_boyAuthor Commented:
Thanks Dex, that works now, could u go over what you did to fix it?

Cheers
DexstarCommented:
Sure.  It's a small list.

1) I moved the definition of the struct to be OUTSIDE of main()
2) I added a semi-colon to the end of the struct definition (you always need that).
3) I changed this:
     node_1->next_ptr = node2;

To this:
     node_1->next_ptr = node_2;

(Node2 isn't a valid name, but node_2 is).

4) I type casted the malloc values by adding (struct node*) to the front of them.  This just tells the compiler to return the returned values as pointers to structs.

I think that's it...

Dex*

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welsh_boyAuthor Commented:
great,
thats cleared a lot up for me..

Cheers again
DexstarCommented:
You're welcome!  Glad to be of help!

Dex*
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