Stack

Stack, from Class 12 Computer Science and the NCERT curriculum, introduces students to one of the most important linear data structures used in computer science. The chapter explains how data structures help organise, store, and access data efficiently, and then focuses on the stack as a structure that follows the Last In First Out (LIFO) principle. Students learn that insertion and deletion of elements occur only at one end called the TOP of the stack. Through familiar examples such as stacks of plates, books, clothes, and boxes, the chapter builds a clear understanding of how stack operations work in everyday life as well as in computing applications.
 

The chapter explores the fundamental stack operations PUSH and POP, along with concepts such as overflow and underflow conditions. Learners study how stacks can be implemented in Python using lists and built-in methods like append() and pop(). Important functions such as checking whether a stack is empty, finding its size, accessing the top element, displaying stack contents, and deleting elements are demonstrated through practical Python programs. The chapter also highlights real-world applications of stacks including undo and redo operations in editors, browser navigation history, reversing strings, function call management, memory allocation, and matching parentheses in arithmetic expressions and programming languages.
 

A major section of the chapter focuses on arithmetic expressions and their representation using infix, prefix (Polish), and postfix (Reverse Polish) notations. Students learn how stacks are used to convert infix expressions into postfix notation and how postfix expressions can be evaluated efficiently using stack-based algorithms. The chapter explains operator precedence, expression parsing, and the role of stacks in compilers and interpreters. By studying stack implementation and applications, learners develop strong skills in algorithm design, logical reasoning, expression evaluation, problem solving, and data structure programming, forming an essential foundation for advanced computer science concepts and software development.