What Is Expression Evaluation in Data Structure?


Scott Campbell

What Is Expression Evaluation in Data Structure?

In the field of data structures, expression evaluation refers to the process of computing the value of an arithmetic or logical expression. This process involves parsing the expression, performing various operations, and returning the final result.

Why is Expression Evaluation important?

Expression evaluation plays a crucial role in various applications such as computer programming, mathematics, and scientific calculations. It allows us to solve complex problems by representing them in a concise and mathematical form.

Types of Expressions

Expressions can be categorized into two main types:

  • Arithmetic Expressions: These expressions involve mathematical operations such as addition, subtraction, multiplication, and division. For example: 5 + 3 * (7 – 2)
  • Logical Expressions: These expressions involve logical operations such as AND, OR, and NOT.

    They are commonly used in programming languages for decision-making and control flow. For example: (x > 5) && (y < 10)

The Expression Evaluation Process

The expression evaluation process can be divided into several steps:

  1. Parsing: In this step, the expression is broken down into its individual components such as operands, operators, and parentheses. This is done using techniques like tokenization and parsing algorithms.
  2. Infix to Postfix Conversion: Infix notation is the standard way of writing expressions where operators are placed between operands (e.g., 5 + 3). However, postfix notation (also known as Reverse Polish Notation) is more suitable for evaluation purposes. In this step, the infix expression is converted to postfix notation using algorithms like the Shunting Yard algorithm.
  3. Evaluation: Once the expression is in postfix notation, it can be evaluated using a stack-based algorithm.

    This involves iterating through each token of the expression and performing appropriate operations based on its type (operand or operator). The operands are pushed onto the stack, and when an operator is encountered, the necessary calculations are performed.

  4. Result: After evaluating all tokens of the expression, the final result is obtained. This can be a numerical value in case of arithmetic expressions or a boolean value in case of logical expressions.


Let’s consider an example to understand the expression evaluation process. We have an arithmetic expression: 4 * (3 + 7).


The expression is parsed into operands ‘4’, ‘*’, ‘(‘, ‘3’, ‘+’, ‘7’, ‘)’.

Infix to Postfix Conversion:

The infix expression ‘4 * (3 + 7)’ is converted to postfix notation as ‘4 3 7 + *’ using the Shunting Yard algorithm.


The postfix expression ‘4 3 7 + *’ is evaluated as follows:

  1. Push operand ‘4’ onto the stack.
  2. Push operand ‘3’ onto the stack.
  3. Push operand ‘7’ onto the stack.
  4. Encounter ‘+’ operator, pop operands ‘3’ and ‘7’, perform addition (result = 10), push result onto stack.
  5. Encounter ‘*’ operator, pop operands ‘4’ and ’10’, perform multiplication (result = 40), push result onto stack.


The final result of the expression ‘4 * (3 + 7)’ is 40.


Expression evaluation is a fundamental concept in data structures that allows us to compute the value of arithmetic and logical expressions. It involves parsing, converting to postfix notation, and performing stack-based evaluation. This process enables us to solve complex problems efficiently and accurately.

By understanding the expression evaluation process, you can enhance your programming skills and tackle more advanced algorithms and data structures with confidence.

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