What Are Stacks in Data Structure?


Scott Campbell

Stacks in Data Structure

A stack is a fundamental data structure in computer science that follows the Last-in, First-out (LIFO) principle. It is an abstract data type that serves as a collection of elements, with two main operations: push and pop.

Basic Operations

Let’s explore the basic operations of a stack:

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

    The newly added element becomes the new top, shifting all other elements down.

  • Pop: This operation removes the topmost element from the stack. The element below it becomes the new top.

Apart from push and pop, stacks also support two additional operations:

  • Peek: This operation returns the value of the topmost element without removing it from the stack.
  • IsEmpty: This operation checks whether the stack is empty or not. It returns true if there are no elements in the stack; otherwise, it returns false.

Main Characteristics

Stacks have some key characteristics that make them useful in various applications:

LIFO Principle

The LIFO principle states that the last item added to a stack will be the first one to be removed. Think of it as stacking plates – you can only remove or add plates from/to the top.

No Random Access

In a stack, we can only access elements from the top; we cannot directly access or modify elements in any other position. This property makes stacks simple yet powerful for certain tasks.

Dynamic Size

Stacks can dynamically grow or shrink as elements are added or removed. This flexibility allows them to be used in situations where the number of elements is not known beforehand.

Applications of Stacks

Stacks find applications in various areas of computer science and software development:

Function Call Stack

A stack is used by compilers and interpreters to manage function calls. When a function is called, its return address and local variables are stored on the stack. This stack-like behavior allows for nested function calls and proper execution flow.

Expression Evaluation

Stacks are commonly used to evaluate arithmetic expressions. Infix, postfix, and prefix notations can all be evaluated using stacks to keep track of operators and operands.

Undo/Redo Operations

In many applications, stacks are used to implement undo and redo functionality. Each action performed is pushed onto a stack, allowing users to undo or redo previous operations by popping elements from the stack.

Browsing History

The browser’s back button functionality can be implemented using a stack. Each visited page is pushed onto the stack, enabling users to navigate backward by popping pages from the stack.

Closing Thoughts

In conclusion, stacks are an essential data structure that follows the LIFO principle. Understanding their basic operations and characteristics will help you utilize them effectively in various programming scenarios. Whether you’re working with function calls or evaluating expressions, stacks offer a simple yet powerful solution for managing data.

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