Re: problem with linked list

From: nrk (ram_nrk2000_at_devnull.verizon.net)
Date: 01/14/04 

Date: Wed, 14 Jan 2004 09:08:57 GMT

David Tandberg-Johansen wrote:

> Hello!
>
> I am an newbie, and I am a litle stuck here. Could anyone please tell me
> what I am doing wrong?
> Here is my code:
>
> #include <stdio>
> #include <stdlib>
>

Smells strongly like another language close to C. You probably want these
to be:
  #include <stdio.h>
  #include <stdlib.h>

> struct node {
> char name[30];

name is an array of 30 characters.

> struct node *next;
> };
> struct node *Head, *new_ptr;
>
> void main(){

main returns int in C.
  int main()

> int length,counter;
> char value[30];
> printf("How many nodes: ");

You need to flush the output stream to ensure that this prompt appears to a
user:
      fflush(stdout);

> scanf("%d",&length);

Need to check return value of scanf to ensure no errors were encountered,
and that length was initialized to a user supplied value.

> Head = NULL;
> for(counter=0; counter<length; counter++){
> new_ptr = malloc(sizeof(struct node));

CLC preferred way of doing this:
          new_ptr = malloc(sizeof *new_ptr);
This avoids hard-coding the type of new_ptr unnecessarily.

> if(new_ptr==NULL){
> printf("not enough memory\n");
> break;
> }
> printf("Enter the name (max 30 chr) for node %d: ",counter);

Again, flush the output stream so that the prompt will appear to the user:
          fflush(stdout);

> scanf("%s",&value);

Ouch!! What you want is:
          scanf("%29s", value);

Note the absence of the & in front of value. Also, since there's a maximum
of 29 characters, we can enforce that as well.

> new_ptr->name = value;

You cannot directly assign to an array in C like this (and this is what your
compiler is telling you). In this case, since your arrays are strings, you
could use strcpy instead:
          strcpy(newptr->name, value);

> new_ptr->next = Head;
> Head = new_ptr;
> }

Remember, main returns int.
     return 0;
> }
>

You also have logic problems with your linked list. You don't retain the
actual starting node of the list as Head.

-nrk.

>
> I am using the Borland c compiler an here is the error message:
> Borland C++ 5.5.1 for Win32 Copyright (c) 1993, 2000 Borland
> C:\c-files\14-1-04\struct4.c:
> Error E2277 C:\c-files\14-1-04\struct4.c 24: Lvalue required in function
> main
> *** 1 errors in Compile ***
>
> I checked up this lvalue in the comp.lang.c FAQ, but i didn't understand
> what concrete i am doing wrong?!
>
> Thanks in advanced
> David

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