1. Computer Science 2 Outline/Learning Objectives for the day:
Review Pre-Post and Infix notation by completing some conversions.
Review dynamics and functions by completing a Dry Run.
Be able to develop an algorithm and code to make a linked list, that is able to put information in order as it is being entered.

2. Warm up Evaluate the following (Assume single digit numbers)
1) – 3 2 * +
2) *
9 2 – 6 * 8 –
Translate the following into postfix and prefix notation
1) ( 5 – x ) + 3(4 + 6y)
2) (2a – 4)/(2b)

3. program DryRunFunOne;
type
ptrtype=^rectype;
rectype=record
num:integer;
next:ptrtype;
end;
var
top, temp:ptrtype;
procedure one(var top:ptrtype);
temp:ptrtype;
count:integer;
begin
for count:=-1 to 2 do
new(temp);
temp^.num:= count*2;
temp^.next:=top;
top:=temp;
function two(top:ptrtype):integer;
begin
if top <> nil then
writeln(top^.num);
two:=top^.num + two(top^.next);
end
else
two:=2;
end;
Begin
top:=nil;
one(top);
writeln(two(top));
readln;
end.

4. Warm-up
Complete the following procedure that should add val to a stack pointed to by top.
Type
pointerType = record
data:real;
next:pointerType;
End;
Procedure add2front(val:real;var top:pointerType);

5. Ordered Insertion into Linked Lists
For example, consider a procedure
insert_in_order(val,top)
that will insert a new value val into linked list top so that sorted order is maintained.
val 9
top 12
nil 7 3 11

6. insert_in_order(val,top) Algorithm
Step 1. Create pointer p, moving p to point to the node after which val should be added.
val 9
top 12
nil 7 3 11 p

7. insert_in_order(val,top) Algorithm
Step 2. Create the new node we want, with the proper data and next values, i.e.
New(temp);
temp^.data := val;
temp^.next := p^.next;
val 9
top 12
nil 7 p 3 11
temp 9

8. insert_in_order(val,top) Algorithm
Step 3. Splice our new node in after the node p points to, i.e.
P^.next = Temp;
val 9
top 12
nil 7 p 3 11 T 9

9. insert_in_order(val,top) Algorithm
And we’re done!
top 12
nil 7 3 11 9

10. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p:=top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
val 9
top 12
nil 7 3 11 p

11. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
val 9
top 12
nil 7 3 11 p

12. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val)do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
val 9
top 12
nil 7 3 11 p

13. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
val 9
top 12
nil 7 3 11 p

14. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
val 9
top 12
nil
New node added to front of sublist whose head is p->next 7 3 11 p

15. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
val 9
top 12
nil
New node added to front of sublist whose head is p->next 7 3 11 p 9

16. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
What if value to be added is less than value of first node in list?
val 2
top 12
nil 7 3 11

17. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val)do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
What if value to be added is less than value of first node in list?
val 2
top 12
nil 7 3 11 p

18. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val)do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
What if value to be added is less than value of first node in list?
val 2
top 12
nil 7 3 11 p

19. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
Not exactly where we wanted- How can we fix this?
val 2
top 12
nil 7 3 11 p 2

20. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val)
begin
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
This will handle the case where new node is to be inserted before first node in list.
Same as add to a stack.
val 2
top 12
nil 7 3 11

21. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val) then
begin
p := top;
while(p^.next^.data < val) do
p := p^.next;
new(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
What if value to be added is larger than value of last node in list?
val 15
top 12
nil 7 3 11

22. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val)then
begin
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
Example: p points to last node in list; p^.next is NIL; evaluation of p^.next^.data will cause program crash
val 15
top 12
nil 7 p 3 11

23. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val) then
begin
p := top;
while(p^.next^.data < val) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
How can we solve this problem?
val 15
top 12
nil 7 p 3 11

24. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val) then
begin
p := top;
while((p^.next <> nil) AND (p^.next^.data < val)) do
p := p^.next;
new(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
Solution: also stop moving p if it's the last node in the list - i.e. if p^.next is nil.
val 15
top 12
nil 7 p 3 11

25. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val)then
begin
p := top;
while((p^.next <> nil) AND (p^.next^.data < val)) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
What if value is to be added to an empty list, i.e. it is the first item to be added to the list?
val 8
top
nil

26. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val) then
begin
p := top;
while((p^.next <> nil) AND (p^.next^.data < val)) do
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
attempt at evaluation of top^.data will cause program crash
val 8
top
nil

27. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if (top^.data < val) then
begin
p := top;
while((p^.next <> nil) AND (p^.next^.data < val))
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
How can we fix this?
val 8
top
nil

28. Implementing insert_in_order(val,L)
Step 1. Create pointer p, moving p to point to the node after which val should be added.
if ((top <> nil) AND (top^.data < val)) then
begin
p := top;
while((p->next != NULL) && (p->next->data < val)) do
p = p->next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top);
Solution: Also check first to make sure list isn’t empty.
val 8
top
nil

29. Putting it all together ...
procedure insert_in_order(val:integer; var top:ptrtype) {
if ((top <> nil) and (top^.data < val)) then
begin
p := top;
while((p^.next <> nil) and (p^.next^.data < val))
p := p^.next;
New(temp);
temp^.data := val;
temp^.next := p^.next;
p^.next = temp;
end
else
add2front(val,top); }
Check to make sure list isn’t empty.
Will handle case where new node is to be inserted before first node in list.
Will handle case where new node is to be inserted at end of the list.

30. First Insertion Linked List Program
Menu
Add
Show
Quit
Pushes
Remove
Save to file
Load from file
Do it recursively!!!

31. Recursive insert_in_order(val,L)
Let’s first look at the base case(s) and see what we do.
Case 1: Inserting value into an empty list.
val 8
top
What do we do?
Add new node containing value to front of list, i.e.
add2front(val, top);

32. Recursive insert_in_order(val,L)
Case 2: Value to be added is smaller than value of first node in list (i.e. top^.data^.val).
val 2
top 12 / 7 3 11
What do we do?
Add new node containing value to front of list, i.e.
add2front(val, top);

33. Recursive insert_in_order(val,L)
Otherwise, will insert value somewhere in sublist pointed to by top^.next
val 8
top 12 / 7 3 11
i.e., insert_in_order(val, top^.next);

34. Recursive insert_in_order(val,L)
Recursive definition for insert_in_order(val,top):
add2front(val,top) if top = nil or top^.data<val
(Base case- empty list or value to be insert_in_order(val, top) = inserted smaller than first item in list)
insert_in_order(val,top^.next) (Recursive case- otherwise)

35. Recursive insert_in_order(val,top)
As a recursive function definition:
procedure insert_in_order(val:real; var top:pointerType);
begin
if (top <> nil and top^.data < val)
insert_in_order(val,top^.next)
else
add2front(val,top);
End;

36. val L procedure insert_in_order(val:real;var top:ptrtype) begin
if (top <> nil and top^.data < val)
insert_in_order(val,top^.next);
else
add2front(val,top);
End;
val 9 L 12 / 7 3 11

37. val L Procedure insert_in_order(val:real;var top:ptrtype) begin
if (top <> nil and top^.data < val)
insert_in_order(val,top^.next);
else
add2front(val,top);
end;
void insert_in_order(double val, Node* &L) {
if (L != NULL && L->data < val)
insert_in_order(val,L->next);
else
add2front(val,L); }
procedure insert_in_order(val:real;var top:ptrtype)
begin
if (top <> nil and top^.data < val)
insert_in_order(val,top^.next);
else
add2front(val,top);
end;
val 9 L 12 / 7 11 3

38. val L Procedure insert_in_order(val:real, var top:pointerType) begin
if (top <> nil and top^.data < val)
insert_in_order(val,>next);
else
add2front(val,L);
end;
void insert_in_order(double val, Node* &L) {
if (L != NULL && L->data < val)
insert_in_order(val,L->next);
else
add2front(val,L); }
procedure insert_in_order(val:real; var top:pointerType)
begin
if (top<> nil and top^.data < val)
insert_in_order(val, top^.next);
else
add2front(val,top);
End;
Procedure insert_in_order(val:real; var top:pointerType)
begin
if (top <> nil and top^.data < val)
insert_in_order(val,top^.next);
else
add2front(val,top);
End;
void insert_in_order(double val, Node* &L) {
if (L != NULL && L->data < val)
insert_in_order(val,L->next);
else
add2front(val,L); }
val 9 L 12 / 7 11 3

39. val L procedure insert_in_order(val:real; var top:pointerType) begin
if (top <> nil and top^.data < val)
insert_in_order(val,top^.next);
else
add2front(val,top);
end;
void insert_in_order(double val, Node* &L) {
if (L != NULL && L->data < val)
insert_in_order(val,L->next);
else
add2front(val,L); }
procedure insert_in_order(val:real, var top:pointerType)
begin
if (top <> nill and top^.data < val)
insert_in_order(val,top^.next);
else
add2front(val,top);
End;
void insert_in_order(double val, Node* &L) {
if (L != NULL && L->data < val)
insert_in_order(val,L->next);
else
add2front(val,L); }
Procedure insert_in_order(val:real; var top:pointerType)
begin
if (top <> nil and top^.data < val)
insert_in_order(val, top^.next);
else
add2front(val,top);
End;
val 9 L 12 / 7 11 3 9

40. val L void insert_in_order(double val, Node* &L) {
Procedure insert_in_order(val:real; var top:pointerType)
begin
if (top <> nil and top^.data < val)
insert_in_order(val, top^.next);
else
add2front(val,top);
End;
void insert_in_order(double val, Node* &L) {
if (L != NULL && L->data < val)
insert_in_order(val,L->next);
else
add2front(val,L); }
procedure insert_in_order(val:real; var top:pointerType)
begin
if (top <> nil and top^.data < val)
insert_in_order(val, top^.next);
else
add2front(val,top);
End;
val 9 L 12 / 7 11 3 9

41. val L procedure insert_in_order( val:real, var top:pointerType) {
if (top <> nil AND top^.data < val)
insert_in_order(val, top^.next);
else
add2front(val,top); }
val 9 L 12 / 7 3 11 9

42. We're Done!
val 9 L 12 / 7 3 11 9