Stack Operations and Implementation
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Questions and Answers

What is the result of evaluating the postfix expression '7 4 -3 * 1 5 + / *'?

  • -2
  • 5 (correct)
  • 7
  • -14

In postfix evaluation, you pop operands from the stack before applying an operator.

True (A)

What do you do when you encounter an operator during postfix evaluation?

Pop operands from the stack, evaluate the operator, and push the result back to the stack.

In postfix notation, the expression '10 2 8 * +' results in _____ after processing all numbers.

<p>18</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Infix = An expression where operators are placed between operands. Postfix = An expression where operators are placed after operands. Stack = A data structure that follows Last In, First Out (LIFO) principle. Operator = A symbol that represents a computation or operation.</p> Signup and view all the answers

What does LIFO stand for in relation to stacks?

<p>Last-In, First-Out (A)</p> Signup and view all the answers

Items removed from a stack are done so in the same order they were inserted.

<p>False (B)</p> Signup and view all the answers

Name one basic operation that can be performed on a stack.

<p>push, pop, peek, isEmpty, or size</p> Signup and view all the answers

To add an element to the top of the stack, the operation performed is called __________.

<p>push</p> Signup and view all the answers

Match the following stack operations with their descriptions:

<p>push = Examine the element at the top of the stack pop = Remove an element from the top of the stack peek = Add an element to the top of the stack isEmpty = Determine whether the stack is empty</p> Signup and view all the answers

What will be the value of 'top' after popping from a stack that currently has 'top = 3'?

<p>2 (D)</p> Signup and view all the answers

The 'isEmpty' operation returns true when there are elements in the stack.

<p>False (B)</p> Signup and view all the answers

Describe how to implement a stack using an array.

<p>Initialize an array and set 'top' to -1. Use 'push' and 'pop' operations to manage elements.</p> Signup and view all the answers

What operation removes the top element from a stack in a linked list implementation?

<p>Pop (B)</p> Signup and view all the answers

Pushing an element onto a stack adds it to the end of the linked list.

<p>False (B)</p> Signup and view all the answers

What is the main data structure used for implementing a stack in the provided content?

<p>Linked List</p> Signup and view all the answers

In a stack, the operation ______ adds an element to the top.

<p>push</p> Signup and view all the answers

Match the actions with their descriptions in stack operations:

<p>Push = Adds an element to the top of the stack Pop = Removes the element from the top of the stack Top = Points to the current top element New Node = Creates a new stack element</p> Signup and view all the answers

Which of the following is NOT a typical application of stacks?

<p>Hold user input (A)</p> Signup and view all the answers

In the reversal of a string using a stack, the last character pushed is the first to be popped.

<p>True (A)</p> Signup and view all the answers

What does the pop operation return in a stack?

<p>The top value of the stack</p> Signup and view all the answers

What action should be taken when encountering a right parenthesis ')'?

<p>Pop operators from the stack until a left parenthesis is encountered. (D)</p> Signup and view all the answers

Infix to postfix conversion does not require considering operator precedence.

<p>False (B)</p> Signup and view all the answers

In the expression (A + (B * C - (D / E^F) * G) * H), what is the final postfix expression?

<p>ABC<em>DEF^/G</em>-H*+</p> Signup and view all the answers

When a reading symbol is an operand, it should be ______ to the result.

<p>printed</p> Signup and view all the answers

Match the following symbols with their respective actions:

<p>Operand = Print to result Left Parenthesis '(', = Push to stack Right Parenthesis ')' = Pop until left parenthesis Operator = Push to stack or Pop based on precedence</p> Signup and view all the answers

In the example expression 10 + 2 * 8 - 3, what happens when the operator * is encountered?

<p>It is pushed onto the stack without popping any operators. (B)</p> Signup and view all the answers

An operator with lower precedence than the stack's top operator gets pushed to the stack.

<p>False (B)</p> Signup and view all the answers

What is the outcome when encountering an operator with higher or equal precedence than the one on the top of the stack?

<p>Pop the operator from the stack and print it to the result.</p> Signup and view all the answers

Flashcards

Stack

A list where items are added and removed from the same end (top).

Push

Adding an element to the top of the stack

Pop

Removing an element from the top of the stack

Peek

Looking at the top element of the stack without removing it

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Stack Implementation (Array)

Using an array to hold stack elements. The stack pointer 'top' tracks the top element

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Stack Implementation (Linked List)

Using a linked list to represent the stack, which allows efficient insertion and deletion at the top.

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isEmpty

A function to check if the stack is empty or not.

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size

A function to get the number of elements within the stack.

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Linked List Implementation of Stack

A stack data structure implemented using a linked list, where the top of the stack is the head of the list.

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Push Operation (Stack)

Adding an element to the top of the stack.

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Pop Operation (Stack)

Removing an element from the top of the stack.

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Stack Applications

Stacks are useful in various applications such as line editing, reversing strings, bracket matching, postfix calculation, function calls, web browser history.

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Reversing a String

A process to reverse the order of characters in a string by using a stack: pushing characters in and popping them out in reversed order.

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Infix to Postfix Conversion

Transforming an infix expression (like a math equation) into a postfix expression, which is suitable for calculations by machines.

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Stack's LIFO property

Last-In, First-Out (LIFO): elements are added to and removed from the top.

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Node Structure (Stack)

Structure for a node in a linked list used to implement a stack, containing data and a pointer to the next node.

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Infix Expression

A mathematical expression where operators are placed between operands (e.g., 10 + 2).

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Postfix Expression

An expression where operators are written after their operands (e.g., 10 2 +).

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Precedence of Operators

The order in which operators are evaluated in an expression (e.g., Multiplication and division have higher precedence than addition and subtraction).

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How to Convert Infix to Postfix

Scan the infix expression, push operands onto the output, handle parentheses and operators based on their precedence, popping operators from the stack to the output.

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Operand

A value used in an operation (e.g., 10, 2, 'A').

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Operator

A symbol that specifies an operation (e.g., +, -, *, /).

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Left Parenthesis '('

Pushes the operator onto the stack when encountered.

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Right Parenthesis ')'

Pops all operators from the stack until a matching left parenthesis is encountered, printing each popped operator to the output stream.

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Evaluate Postfix Expression

Process of calculating the result of a postfix expression using a stack.

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Stack in Postfix Evaluation

A stack is used in evaluating postfix expressions to store operands and intermediate results.

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Why Postfix?

Postfix expressions are easier for computers to evaluate because they avoid the need for parentheses and complex operator precedence rules.

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Study Notes

Stacks

  • Stacks are lists with the restriction that insertions and deletions occur at the same end.
  • Elements are added and removed in a Last-In, First-Out (LIFO) manner.
  • Operations on a stack include: push (add), pop (remove), and peek (retrieve top element).
  • Stacks are useful when the order of operations must be reversed.

Stack Operations

  • push: Adds an element to the top of the stack.
  • pop: Removes an element from the top of the stack.
  • peek: Retrieves the top element of the stack.
  • isEmpty: Checks if the stack is empty.
  • size: Returns the number of elements in the stack.

Stack Implementation (Using Arrays)

  • A fixed-size array is used to store stack elements.
  • A variable top keeps track of the index of the top element.
  • top is initialized to -1 when the stack is empty.
  • push increments top and stores the new element at stack[top].
  • pop retrieves the element at stack[top], decrements top, and returns the element.
  • MAXSIZE defines the maximum size of the array.

Stack Implementation (Using Linked Lists)

  • A dynamic structure (using pointers).
  • A Node structure, containing data and a pointer to the next Node.
  • top points to the top element (head of the list).
  • push inserts a new node at the beginning of the list.
  • pop removes the node at the beginning of the list.

Stack Applications

  • String reversal: Pushing characters into a stack and then popping them out reverses them.
  • Bracket matching: Using a stack for parenthesis checks. If a closing bracket is encountered and corresponding opening bracket is not present in the stack, there is a mismatch.
  • Postfix Evaluation: Evaluating expressions written in postfix notation (e.g., 10 2 +).
  • Function calls: Tracking function calls in programming.
  • Browsers: Storing visited pages in a LIFO manner.

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Related Documents

Lecture 4 - Stacks PDF

Description

Explore the fundamental concepts of stacks, including LIFO behavior and essential operations like push, pop, and peek. Understand stack implementation using arrays and learn how to manage size and check for emptiness. This quiz will test your knowledge on the essential operations and structure of stacks.

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