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Linked Lists

The following program creates a singly linked list. Pointers are maintained to the head and tail of the list.

Figure 2: Linked List

#include <stdio.h>

typedef struct _list_item {
  int val;
  struct _list_item *next;
} list_item;

/* prototypes */
list_item *add_list_item(list_item *entry, int value);
void print_list_items(void);

list_item *head=NULL;
list_item *tail=NULL;

main(int argc, char *argv[])
{
  tail=add_list_item(tail,5);
  tail=add_list_item(tail,7);
  tail=add_list_item(tail,2);

  print_list_items();
}

list_item *add_list_item(list_item *entry, int value)
{
  list_item *new_list_item;

  new_list_item=(list_item*)malloc(sizeof(list_item));
  if (entry==NULL){
    head=new_list_item;
    printf("First list_item in list\n");
  }
  else {
    entry->next = new_list_item;
    printf("Adding %d to list. Last value was %d \n",value,entry->val);
  }
  new_list_item->val  = value;
  new_list_item->next = NULL;
  return new_list_item;
}

void print_list_items(void)
{
  list_item *ptr_to_list_item;

  for (ptr_to_list_item= head;ptr_to_list_item!= NULL; 
           ptr_to_list_item=ptr_to_list_item->next) {
    printf("Value is %d \n", ptr_to_list_item->val);
  }
}