linked list recursive help

[dreamkk]

for example :
link a:5->4->3->2->1->NULL
link b: NULL

typedef struct node* link;
struct node { int item; link next; };
....
link no_scan(int n, link a, link b)
{
    int n1;
    link xs1, xs2, c = NULL;
    if(n == 0)
    {
        b = a;
        return NULL;
    }

    if(n == 1)
    {
        b = a->next;      //here will be th problem
        a->next = NULL;
        return a;
    }
    n1 = n/2;
    xs1 = no_scan(n1,a,b);
    xs2 = no_scan((n-n1),b,c);   ///when i hit here, error, cos i pass(1,NULL,NULL);
    b = c;
    return merge(xs1,xs2);
}

i wanna make sure b has changed in the call no_scan(n1,a,b);
can anyone one help me, thanks a lot

[DavT]

You can't change the inputs to a function in this way. For example:

void f(int n)
{
  n = 49;
}

void g (int * pN)
{
  *pN = 345;
}

int main (void)
{
  int n = 20;

  f(n);
  printf("after f(n), n is now: %d\n", n);

  g(&n);
  printf("after g(&n), n is now: %d\n", n);

  return 0;
}

/*
output:
after f(n), n is now: 20
after g(&n), n is now: 345
*/

I think that may be your problem...

[Shiro]

Variable b is a pointer, if you want to change a pointer, you need to pass the address of the pointer. The function header would then look like this:

link no_scan(int n, link a, link *b)

[dreamkk]

thanks a lot