- Because a linked list is a sequential data structure,
when you want to insert a new element into a linked list,
you must first find the location in the list
before you can insert the element.
- The easiest way to insert a new element into
a linked list is at the start --- because the linked
list is accessed from the beginning (the first element of the list
is very easy to find :-))...
- NOTE: Although insert at the start of a list is easy to do, it may be desirable to insert new elements elsewhere because we want to achieve another more important objective....
- The empty list is always represented
as follows:
- This can be accomplished by the following statement:
ListElem head = NULL;
- Unlike array elements that are created statically
by a variable definition
(such as float A[3][4]),
new list elements are "created" dynamically.
- You have seen variables being created by variable definitions
- In addition, new variables can be created by
the new operator in C++.
- Syntax of the
new operator
Syntax: new TYPE;
Example of usage: ListElem *p; p = new ListElem;
- The new operator
operates on a type.
- The new operator
will reserve
an amount of memory space ("create variable") to store
the values of a new variable of the given type.
- When the space is reserved, the
new operator
returns the (first) address of the reserved memory as
its result
(BTW, you have seen an operator that return a memeory address: the & operator...)
- The new operator
operates on a type.
- Now we know everything that we need to know to
insert a new list element at the start of the list:
Overview inserting new elements at start of a list: (1) Make a new list element: ListElem *elem; elem = new ListElem; (2) Fill the information portion of the list element: elem->value = 1500; (3) Link new element at start of list: elem.next = head; // Make new list element points // to the start of "old list" head = elem; // Make "head" points to // the **new** starting object
- This is what happens if we insert the first element into
an (empty) list:
- This is what happens if we insert the new element into
a non-empty list:
- Example Program:
(Demo insertion at HEAD of list) ----
click here
