Singly-linked list/Element definition

Define the data structure for a singly-linked list element. Said element should contain a data member capable of holding a numeric value, and the link to the next element should be mutable.

Ada

type Link;
type Link_Access is access Link;
type Link is record
   Next : Link_Access := null;
   Data : Integer;
end record;

C

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

C++

The simplest C++ version looks basically like the C version:

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

Initialization of links on the heap can be simplified by adding a constructor:

struct link
{
  link* next;
  int data;
  link(int a_data, link* a_next = 0): next(a_next), data(a_data) {}
};

With this constructor, new nodes can be initialized directly at allocation; e.g. the following code creates a complete list with just one statement:

link* small_primes = new link(2, new link(3, new link(5, new link(7))));

However, C++ also allows to make it generic on the data type (e.g. if you need large numbers, you might want to use a larger type than int, e.g. long on 64-bit platforms, long long on compilers that support it, or even a bigint class).

template<typename T> struct link
{
  link* next;
  T data;
  link(int a_data, link* a_next = 0): next(a_next), data(a_data) {}
};

Note that the generic version works for any type, not only integral types.

Delphi / Object Pascal / Turbo Pascal / Standard Pascal

A simple one way list. I use a generic pointer for the data that way it can point to any structure, individual variable or whatever.

  Type
    pOneWayList = ^OneWayList;
    OneWayList = record
                  pData : pointer ;
                  Next  : pOneWayList ;
                 end;