Infix to Postfix Conversion Using Stack in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack.

DSA Javascript

stack.[1](element);

Drag options to blanks, or click blank then click option'

Apush

Bpop

Cshift

Dunshift

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of push() removes an element instead of adding.

Using shift() or unshift() modifies the start of the array, not the end.

The push() method adds an element to the top of the stack (array).

2fill in blank

medium

Complete the code to check if the stack is empty.

DSA Javascript

if (stack.[1] === 0) { return true; } else { return false; }

Drag options to blanks, or click blank then click option'

Asize

Blength

Ccount

Dempty

Attempts:

3 left

💡 Hint

Common Mistakes

Using size or count which are not valid properties for JavaScript arrays.

Using empty which is not a property.

The length property gives the number of elements in an array (stack).

3fill in blank

hard

Fix the error in popping the top element from the stack.

DSA Javascript

let top = stack.[1]();

Drag options to blanks, or click blank then click option'

Apush

Bpeek

Cpop

Dtop

Attempts:

3 left

💡 Hint

Common Mistakes

Using push() adds an element instead of removing.

peek() and top() are not standard JavaScript array methods.

pop() removes and returns the last element from the stack.

4fill in blank

hard

Fill both blanks to correctly check operator precedence.

DSA Javascript

function precedence(op) {
  if (op === '+' || op === '-') return [1];
  if (op === '*' || op === '/') return [2];
  return 0;
}

Drag options to blanks, or click blank then click option'

A1

B2

C3

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning the same precedence to all operators.

Confusing precedence values.

Addition and subtraction have precedence 1; multiplication and division have precedence 2.

5fill in blank

hard

Fill all three blanks to correctly convert infix to postfix for an operator.

DSA Javascript

while (stack.length > 0 && precedence(stack[stack.length - 1]) [1] precedence(token)) {
  output.push(stack.[2]());
}
stack.[3](token);

Drag options to blanks, or click blank then click option'

A<=

B>=

Cpop

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<=' instead of '>=' causes wrong order of operators.

Using push() instead of pop() to remove elements.

Forgetting to push the current token after popping.

We pop from stack while top has higher or equal precedence, then push the current token.

Practice

1. What is the main purpose of using a stack in Infix to Postfix Conversion?

easy

A. To temporarily hold operators and manage their precedence

B. To store the final postfix expression

C. To reverse the infix expression

D. To count the number of operands

Solution

1. Step 1: Understand the role of stack in conversion

   The stack is used to hold operators temporarily while scanning the infix expression to respect operator precedence and associativity.

2. Step 2: Differentiate stack usage from other tasks

   The postfix expression is built separately, and the stack is not used to store operands or reverse the expression.

3. Final Answer:

   To temporarily hold operators and manage their precedence -> Option A

4. Quick Check:

   Stack holds operators [OK]

Hint: Stack holds operators to manage precedence during conversion [OK]

Common Mistakes:

• Thinking stack stores operands
• Confusing stack role with reversing expression
• Assuming stack counts operands

2. Which of the following is the correct way to check if the stack is empty in JavaScript during infix to postfix conversion?

easy

A. if (stack === undefined)

B. if (stack == null)

C. if (stack.length === 0)

D. if (stack.isEmpty())

Solution

1. Step 1: Recall JavaScript array properties

   Stacks are usually implemented using arrays; checking if stack.length === 0 confirms if it is empty.

2. Step 2: Evaluate other options

   stack == null or stack === undefined check if the variable exists, not if it's empty. stack.isEmpty() is not a built-in method in JavaScript arrays.

3. Final Answer:

   if (stack.length === 0) -> Option C

4. Quick Check:

   Array length zero means empty stack [OK]

Hint: Use stack.length === 0 to check empty stack in JavaScript [OK]

Common Mistakes:

• Using undefined or null checks instead of length
• Calling non-existent isEmpty() method
• Confusing variable existence with emptiness

3. What is the postfix expression output for the infix expression A + B * C using stack-based conversion?

medium

A. ABC*+

B. AB+C*

C. A+BC*

D. *ABC+

Solution

1. Step 1: Apply operator precedence rules

   Multiplication (*) has higher precedence than addition (+), so B * C is evaluated first.

2. Step 2: Convert to postfix step-by-step

   Postfix for B * C is BC*. Then add A and + operator: ABC*+.

3. Final Answer:

   ABC*+ -> Option A

4. Quick Check:

   Multiplication before addition = ABC*+ [OK]

Hint: Multiply before add; postfix puts operator after operands [OK]

Common Mistakes:

• Ignoring operator precedence
• Placing operators before operands
• Mixing operand order

4. Identify the error in this JavaScript snippet for infix to postfix conversion:

if (stack.length = 0) { output += token; }

medium

A. Output variable is not declared

B. Missing semicolon after if condition

C. Stack length property is incorrect

D. Assignment operator used instead of comparison

Solution

1. Step 1: Check the if condition syntax

   The condition uses single equals = which assigns 0 to stack.length instead of comparing it.

2. Step 2: Understand correct comparison operator

   Use === or == to compare values, not =.

3. Final Answer:

   Assignment operator used instead of comparison -> Option D

4. Quick Check:

   Use === for comparison, not = [OK]

Hint: Use === for comparison, not = assignment [OK]

Common Mistakes:

• Using = instead of === in conditions
• Ignoring syntax errors in if statements
• Assuming missing semicolon causes error here

5. Given the infix expression (A + B) * (C - D) / E, what is the correct postfix expression after conversion using stack?

hard

A. AB+CD-E*/

B. AB+CD-*E/

C. AB+CD-E/*

D. AB+CD*E/-

Solution

1. Step 1: Convert each parenthesis group separately

   (A + B) becomes AB+, and (C - D) becomes CD-.

2. Step 2: Apply multiplication and division in order

   Multiply results: AB+ CD- *, then divide by E: AB+CD-*E/.

3. Final Answer:

   AB+CD-*E/ -> Option B

4. Quick Check:

   Parentheses handled first, then * and / left to right [OK]

Hint: Handle parentheses first, then * and / left to right [OK]

Common Mistakes:

• Ignoring parentheses order
• Mixing operator precedence
• Placing division before multiplication incorrectly