Build the list {1,2,3} with the minimum assignment statements in C

Question

Rewrite this to minimize the assignment statements

/*
 Build the list {1, 2, 3} in the heap and store
 its head pointer in a local stack variable.
 Returns the head pointer to the caller.
*/
struct node* BuildOneTwoThree() {
struct node* head = NULL;
struct node* second = NULL;
struct node* third = NULL;
head = malloc(sizeof(struct node)); // allocate 3 nodes in the hea
second = malloc(sizeof(struct node));
third = malloc(sizeof(struct node));
head->data = 1; // setup first node
head->next = second; // note: pointer assignment rule
second->data = 2; // setup second node
second->next = third;
third->data = 3; // setup third link
third->next = NULL;
// At this point, the linked list referenced by "head"
// matches the list in the drawing.
return head;
}

From http://cslibrary.stanford.edu/

Answer 1

Generalizing:

node* buildNodeList(unsigned int n)
{
    node * head;
    node * prev;
    if (n == 0)
    {
        return 0;
    }

    prev = 0;
    while (n > 0)
    {
        head = (node*)malloc(sizeof(node));
        head->data = n;
        head->next = prev;
        prev = head;
        --n;
    }

    return head;
}

Answer 2

node *head;
node **next= &head;

int next_value= 1;
while (next_value<=3)
{
    *next= malloc(sizeof(struct node));
    (*next)->data= next_value;
    next= &(*next)->next;
    ++next_value;
}

*next= 0;

Answer 3

Two assignments; complete compilable code follows :-)

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

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

struct node *newnode(int val, int nextval) {
  struct node *x = malloc(sizeof *x);  /* not assignment: initialization */
  if (x == NULL) {
    fprintf(stderr, "oops, no memory\n");
    exit(EXIT_FAILURE);
  }
  x->data = val;                                           /* assignments: 1 */
  x->next = (nextval < 4)                                  /* assignments: 2 */
          ? (newnode(nextval, nextval+1))
          : (NULL);
  return x;
}

int main(void) {
  struct node *head = newnode(1, 2); /* not assignment: initialization */
  struct node *curr;

  /* building of the list (3 elements with `data` values from 1 to 3) done */
  /* the assignments after this line are not used to BUILD the list */

  /* use nodes */
  curr = head;
  while (curr) {
    printf(" %d ==>", curr->data);
    curr = curr->next;
  }

  /* free structures */
  curr = head;
  while (curr) {
    struct node *tmp = curr->next;
    free(curr);
    curr = tmp;
  }

  return 0;
}

Answer 4

More general:

#include <stdarg.h>

node *BuildList(int len, ...)
{
    va_list args;
    node *head, **p = &head;
    va_start(args, len);
    while(len--) {
        *p = malloc(sizeof(node));
        (*p)->data = va_arg(args, int);
        p = &(*p)->next;
    }
    *p = 0;
    va_end(args);
    return head;
}