Page 142 - DCAP201_FUNDAMENTALS_OF_DATA_STRUCTURES

Unit 9: Stacks

Notes
Figure 9.3: Shipment in a Cargo

Source: http://www.tup.tsinghua.edu.cn/Resource/tsyz/034111-01.pdf
Figure 9.4 shows the schematic diagram of a stack.

Figure 9.4: Schematic Diagram of a Stack

Source: http://www.tup.tsinghua.edu.cn/Resource/tsyz/034111-01.pdf
Other names for a stack are pushdown list, and LIFO (or) Last In First Out list. The stack allows
access to only one item, i.e. the last item inserted. In the schematic diagram of a stack, after
inserting Item 4 into the stack, it acts as the topmost element. It will be removed first. The very
first item that was inserted into the stack is Item 1. It will be removed as the last item.

Self Assessment

Fill in the blanks:
1. A ....................... is an ordered collection of homogeneous data elements where the insertion
and deletion operations occur at one end only, called the top of the stack.
2. The stack allows access to only one item, i.e. the last item inserted. This is also known as
....................... system.

9.2 Operations on Stacks

The primitive operations that can be performed on a stack are given below:
1. Inserting an element into the stack (PUSH operation)
2. Removing an element from the stack (POP operation)
3. Determining the top item of a stack without removing it from the stack (PEEP operation)

PUSH operation is used to insert the data elements in a stack. The push operation inserts an
element on to a stack and the element inserted settles down on the stack. Practically saying, a
stack can be an array where elements are inserted in LIFO fashion.

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