Stack operations performed on stack stack applications Infix to postfix conversion Infix to prefix conversion Postfix to infix conversion Prefix to infix conversion algorithm to push an element in a stack algorithm to pop an element from a stack

1. Chapter 4Chapter 4
staCksstaCks
03/17/18 BY MS. SHAISTA QADIR 1
PRESENTED BY
Shaista Qadir
Lecturer king khalid university

2. CONteNtsCONteNts
 staCk
 OperatiONs perfOrmed ON staCk
 staCk appliCatiONs
 iNfix tO pOstfix CONversiON
 iNfix tO prefix CONversiON
 pOstfix tO iNfix CONversiON
 prefix tO iNfix CONversiON
 algOrithm tO push aN elemeNt iN a staCk
 algOrithm tO pOp aN elemeNt frOm a
staCk
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3. staCkstaCk
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 A stack is a linear data structure that can be accessed only
at one of its ends for storing and retrieving data.
 Such a stack resembles a stack of trays in a cafeteria: New
trays are put on the top of the stack and taken off the top.
 The last tray put on the stack is the first tray removed from
the stack.
 For this reason, a stack is called an LIFO structure last
in/first out.

4. OperatiONs perfOrmed ONOperatiONs perfOrmed ON
staCkstaCk
03/17/18 BY MS. SHAISTA QADIR 4
 The operations are as follows:
◦ clear() : Clear the stack.
◦ isEmpty() : Check to see if the stack is empty.
◦ push(el) : Put the element el on the top of the
stack.
◦ pop() : Take the topmost element from the
stack.
◦ topEl() : Return the topmost element in the
stack without removing it.

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Stack Overflow:
If adding an element onto the top of the stack and if that
stack is full this situation is called stack overflow.
Stack Underflow:
Removing an element from the stack and if that stack is
empty this situation is called stack underflow
OperatiONs perfOrmed ON
staCk

6. staCk appliCatiONsstaCk appliCatiONs
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APPLICATIONS OF STACK:
◦ Reversing Data: We can use stacks to reverse data.
(example: files, strings) Very useful for finding
palindromes.
◦ To evaluate Arithmetic expressions: (Prefix, Infix, Postfix
Notations)
◦ Arithmetic expressions have
 Operands (variables or numeric constants).
 Operators
 i. Binary : +, -, *, / ,%
 ii. Unary: - (sign for negative numbers)

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 Example:
Prefix Notation Infix Notation Postfix Notation
+A * B C A + B * C A B C * +
* + A B C (A+B) * C A B + C *
+ – A B C A – B + C A B – C +
– A + B C A – (B+C) A B C + –
*+AB-CD (A+B)*(C-D) AB+CD-*
 Priority convention(Rules):
◦ Unary minus has Highest priority
◦ *, /, % have Medium priority
◦ +, - have Lowest priority
stack applicationsstack applications

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stack applicationsstack applications
Infix Expression Prefix Expression Postfix Expression
A + B * C + D + + A * B C D A B C * + D +
(A + B) * (C + D) * + A B + C D A B + C D + *
A * B + C * D + * A B * C D A B * C D * +
A + B + C + D + + + A B C D A B + C + D +

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stack applicationsstack applications
Example:
To evaluate the expression A+B*C using Postfix notation in
a
Stack
Postfix notation for A+B*C is ABC*+
PUSH A
PUSH B
PUSH C
MULTIPLY
ADD
POP
PUSH A PUSH B PUSH C MULTIPLY ADD POP

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Postfix to Infix conversionPostfix to Infix conversion
Example: abc-+de-fg-h+/* to infix

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Postfix to Infix conversionPostfix to Infix conversion
Example: abc-+de-fg-h+/* to infix (contd)

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Postfix to Infix conversionPostfix to Infix conversion
Example: abc-+de-fg-h+/* to infix (contd)

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Prefix to Infix conversionPrefix to Infix conversion
Example: *+a-bc/-de+-fgh to infix

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Prefix to Infix conversionPrefix to Infix conversion
Example: *+a-bc/-de+-fgh to infix (contd)

18. algorithm to push analgorithm to push an
element in a stackelement in a stack
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ALGORITHM:
1. If (TOP == MAX-1) Then
2. Print: Overflow
3. Else
4. Set TOP = TOP + 1
5. Set STACK[TOP] = ITEM
6. Print: ITEM inserted EndIf
7. Exit.

19. algorithm to push analgorithm to push an
elementelement
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PROGRAM LOGIC:
public boolean isFull()
{
if(top == maxsize-1)
return true;
else
return false;
}
public void push(int a)
{
++top;
arr[top] = a;
}

20. algorithm to pop analgorithm to pop an
element From staCKelement From staCK
03/17/18 BY MS. SHAISTA QADIR 20
ALGORITHM:
1. If (TOP == -1) Then
2. Print: Underflow
3. Else
4. Set ITEM = STACK[TOP]
5. Set TOP = TOP - 1
6. Print: ITEM deleted EndIf
7. Exit

21. algorithm to pop analgorithm to pop an
element From staCKelement From staCK
03/17/18 BY MS. SHAISTA QADIR 21
PROGRAM LOGIC:
public boolean isEmpty()
{
if(top == -1)
return true;
else
return false;
}
public int pop ()
{
int e = arr[top];
top--;
return e;
}

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THANK YOUTHANK YOU