Which Data Structure Is Used for Evaluation of Postfix Expression?


Heather Bennett

The evaluation of postfix expressions is a common task in computer science and programming. Postfix expressions, also known as Reverse Polish Notation (RPN), are mathematical expressions in which the operands are placed before their operators. For example, the infix expression “3 + 4” would be written as “3 4 +” in postfix notation.

To evaluate a postfix expression, a data structure called a stack is commonly used. A stack is a Last-In-First-Out (LIFO) data structure that allows for efficient insertion and removal of elements from one end, known as the top.

Let’s take a closer look at how a stack can be used to evaluate postfix expressions.

Stack Data Structure:

In HTML, we can use the tag to emphasize important concepts. In this case, the stack data structure plays a crucial role in evaluating postfix expressions.

A stack supports two primary operations:

1. Push: This operation adds an element to the top of the stack.

2. Pop: This operation removes and returns the topmost element from the stack.

To evaluate a postfix expression using a stack, we follow these steps:

1. Create an empty stack. 2. Scan the expression from left to right. 3. If an operand (number) is encountered, push it onto the stack. 4. If an operator is encountered, pop the top two elements from the stack.

5. Perform the operation using the operator on those two elements. 6. Push the result back onto the stack. 7. Repeat steps 4-6 until all elements have been scanned. 8. The final result will be left on top of the stack.


Let’s consider an example to illustrate this approach further:

Postfix expression: “5 3 +”

Step 1: Create an empty stack.

Step 2: Scan from left to right.

– Encounter “5”: Push 5 onto the stack. – Encounter “3”: Push 3 onto the stack.

– Encounter “+”: Pop 3 and 5 from the stack. Perform the addition: 3 + 5 = 8. Push the result, 8, onto the stack.

Step 3: All elements have been scanned. The final result, 8, is left on top of the stack.

Implementation in HTML:

We can implement this algorithm in HTML using JavaScript. Let’s write a function that takes a postfix expression as input and returns its evaluated result:



This JavaScript function uses an array as a makeshift stack. It iterates over each element of the postfix expression and performs appropriate push and pop operations based on whether an operand or operator is encountered. Finally, it returns the evaluated result.


In conclusion, the data structure used for evaluating postfix expressions is a stack. By following a systematic approach of scanning the expression and performing operations using operands and operators from the top of the stack, we can efficiently evaluate postfix expressions.

By utilizing the , ,

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  • tags in HTML, we can emphasize key concepts and present information in a visually engaging manner. Understanding the stack data structure and its role in evaluating postfix expressions is essential for any programmer or computer science enthusiast.