-
8/3/2019 Stacks Son
1/21
EASTERN MEDITERRANEAN UNIVERSITY
Stacks
EENG212 Algorithms and Data Structures
-
8/3/2019 Stacks Son
2/21
Stacks
Outline
Stacks
Definition
Basic Stack Operations
Array Implementation of Stacks
-
8/3/2019 Stacks Son
3/21
What is a stack?
It is an ordered group of homogeneous items of elements.
Elements are added to and removed from the top of the stack(the
mostrecently added items are at the top of the stack).
The last element to be added is the first to be removed
(LIFO:Last In, First Out).
-
8/3/2019 Stacks Son
4/21
BASIC STACK OPERATIONS
Initialize the Stack.
Pop an item off the top of the stack (delete anitem)
Push an item onto the top of the stack (insertan item)
Is the Stack empty?
Is the Stack full? Clear the Stack
Determine Stack Size
-
8/3/2019 Stacks Son
5/21
Array Implementation of the Stacks
The stacks can be implemented by the use ofarraysand linked
lists.
One way to implement the stack is to have a
data structure where a variable called topkeeps the location of
the elements in the stack(array)
An array is used to store the elements in the
stack
-
8/3/2019 Stacks Son
6/21
Stack Definition
struct STACK{
int count; /* keeps the number of elements inthe stack */
int top; /* indicates the location of the top ofthe stack*/
int items[STACKSIZE]; /*array to store the
stack elements*/}
-
8/3/2019 Stacks Son
7/21
Stacks
-
8/3/2019 Stacks Son
8/21
Stack Initialisation
initialize the stack by assigning -1 to the toppointer to
indicate that the array based stackis empty (initialized) as
follows:
You can write following lines in the mainprogram:
:
STACK s;
s.top = -1;
:
-
8/3/2019 Stacks Son
9/21
Stack Initialisation
Alternatively you can use the followingfunction:
void StackInitialize(STACK *Sptr)
{
Sptr->top=-1;
}
-
8/3/2019 Stacks Son
10/21
Push Operation
Push an item onto the top of the stack (insert an item)
-
8/3/2019 Stacks Son
11/21
Void push (Stack *, type newItem)
Function: Adds newItem to the top ofthe stack.
Preconditions: Stack has beeninitialized and is not full.
Postconditions: newItem is at the top ofthe stack.
-
8/3/2019 Stacks Son
12/21
void push (STACK *, type newItem)
void push(STACK *Sptr, int ps) /*pushes ps intostack*/
{if(Sptr->top == STACKSIZE-1){
printf("Stack is full\n");return; /*return back to main
function*/
}else {
Sptr->top++;
Sptr->items[Sptr->top]= ps;Sptr->count++;
}}
-
8/3/2019 Stacks Son
13/21
Pop operation
Popan item off the top of the stack (deletean item)
-
8/3/2019 Stacks Son
14/21
type pop (STACK *)
Function: Removes topItem from stack andreturns with topItem
Preconditions: Stack has been initialized and
is not empty. Postconditions: Top element has been
removed from stack and the function returnswith the top
element.
-
8/3/2019 Stacks Son
15/21
Type pop(STACK *Sptr)
int pop(STACK *Sptr){int pp;if(Sptr->top == -1){
printf("Stack is empty\n");
return -1; /*exit from the function*/}else {
pp = Sptr->items[Sptr->top];Sptr->top--;
Sptr->count--;return pp;
}}
-
8/3/2019 Stacks Son
16/21
void pop(STACK *Sptr, int *pptr)
void pop(STACK *Sptr, int *pptr){if(Sptr->top == -1){
printf("Stack is empty\n");
return;/*return back*/}else {
*pptr = Sptr->items[Sptr->top];Sptr->top--;
Sptr->count--;}}
-
8/3/2019 Stacks Son
17/21
EXAMPLE
The following program implements stack ofsize 10 using array
representation.
The 10 elements entered by the user are
pushed into the stack and then the elementsare popped back and
displayed.
-
8/3/2019 Stacks Son
18/21
#include
#include
#define STACKSIZE 10
typedef struct{int count;
int top;
int items[STACKSIZE]; /*stack can contain up to 10
integers*/
}STACK;
void push(STACK *, int);
int pop(STACK *);
int main()
{
int p, i;STACK s;
s.top = -1; /*indicates that the stack is empty at the
beginning*/
s.count = 0; /* 0 items are in the stack*/
-
8/3/2019 Stacks Son
19/21
/*reading and pushing items into the stack*/
printf("Enter the %d stack items\n",STACKSIZE);
for(i=0;i
-
8/3/2019 Stacks Son
20/21
void push(STACK *Sptr, int ps) /*pushes ps into stack*/
{
if(Sptr->top == STACKSIZE-1){
printf("Stack is full\n");
printf("There are %d items in the stack\n", Sptr-
>count);
return; /*return back to main function*/
}
else {Sptr->top++;
Sptr->items[Sptr->top]= ps;
Sptr->count++;
}
}
-
8/3/2019 Stacks Son
21/21
int pop(STACK *Sptr){
int pp;
if(Sptr->top == -1){
printf("Stack is empty\n");return -1 /*exit from the
function*/
}
else {
pp = Sptr->items[Sptr->top];
Sptr->top--;Sptr->count--;
return pp;
}
}
