Stack Data Structure: Implementation and Uses, Exams of Biology

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Stacks

CS 308 – Data Structures

What is a stack?

• It is an ordered group of homogeneous items of elements.
• Elements are added to and removed from the top of the stack (the most recently added items are at the top of the stack).
• The last element to be added is the first to be removed ( LIFO : Last In, First Out).

Push (ItemType newItem)

• Function : Adds newItem to the top of the stack.
• Preconditions : Stack has been initialized and is not full.
• Postconditions : newItem is at the top of the stack.

Pop (ItemType& item)

• Function : Removes topItem from stack and

returns it in item.

• Preconditions : Stack has been initialized

and is not empty.

• Postconditions : Top element has been

removed from stack and item is a copy of

the removed element.

Stack Implementation #include "ItemType.h" // Must be provided by the user of the class // Contains definitions for MAX_ITEMS and ItemType class StackType { public: StackType(); void MakeEmpty(); bool IsEmpty() const; bool IsFull() const; void Push(ItemType); void Pop(ItemType&); private: int top; ItemType items[MAX_ITEMS]; };

Stack Implementation (cont.) StackType:: StackType() { top = -1; } void StackType:: MakeEmpty() { top = -1; } bool StackType:: IsEmpty() const { return (top == -1); }

Stack overflow

• The condition resulting from trying to push

an element onto a full stack.

if(!stack.IsFull())

stack.Push(item);

Stack underflow

• The condition resulting from trying to pop

an empty stack.

if(!stack.IsEmpty())

stack.Pop(item);

Implementing stacks using templates

• Templates allow the compiler to generate

multiple versions of a class type or a

function by allowing parameterized types.

• It is similar to passing a parameter to a

function (we pass a data type to a class !!)

Example using templates

// Client code

StackType myStack;

StackType yourStack;

StackType anotherStack;

myStack.Push(35);

yourStack.Push(584.39);

The compiler generates distinct class types and gives its own internal name to each of the types.

Function templates

• The definitions of the member functions must be

rewritten as function templates.

template StackType:: StackType () { top = -1; } template void StackType:: MakeEmpty () { top = -1; }

Function templates (cont.) template void StackType:: Pop (ItemType& item) { item = items[top]; top--; }

Comments using templates

• The^ template^ designation must precede the class method name in the source code for each template class method.
• The word^ class^ is required by the syntax of the language and does not mean that the actual parameter must be the name of a class.
• Passing a parameter to a template^ has an effect at compile time.

Implementing stacks using dynamic array allocation (cont.) template StackType:: StackType (int max) { maxStack = max; top = -1; items = new ItemType[max]; } template StackType::~ StackType () { delete [ ] items; }

Example: postfix expressions

• Postfix notation is another way of writing arithmetic

expressions.

• In postfix notation, the operator is written after the

two operands.

infix : 2+5 postfix : 2 5 +

• Expressions are evaluated from left to right.
• Precedence rules and parentheses are never needed!!