Ch 3Stack — Class 12 Computer Science, concept-first.

In Class XI, you learned about Python's built-in data types like strings, lists, tuples, and sets. These are not just random containers — they are examples of data structures.

A stack is a linear arrangement of elements where all additions and removals happen from the same end — the top. Think of a pile of plates in a kitchen or a stack of books on a table (Figure 3.1).

A stack is a data structure that follows the Last In, First Out (LIFO) principle — the last item added is the first one removed.

A stack is a structure that implements the LIFO arrangement introduced in the previous section, hence elements are added to and deleted from the stack at one end only.

The two fundamental operations on a stack are PUSH and POP. They are the only ways to insert or remove data, and they strictly enforce the LIFO (Last In, First Out) order.

A stack is an ordered, linear collection where all insertions and deletions happen at one end — the top. In Python, the simplest way to build a stack is to use the built-in list type.

We write arithmetic expressions in a natural way, placing operators like +, -, , / between their operands. For example, x + y or 2 - 3 y.

Humans naturally understand infix expressions like x + y / z. We know from the BODMAS rule that division has higher precedence than addition, so we evaluate y / z first, even though the + operator app…

When you evaluate an arithmetic expression, the usual way — with operators between operands, like 7 + 8 — is called infix notation.

- Stack is a data structure in which insertion and deletion is done from one end only, usually referred to as TOP.