INFSCI 0015 Data Structures Lecture 17: Stack

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INFSCI 0015 - Data StructuresLecture 17 Stack

• Peter Brusilovsky
• http//www2.sis.pitt.edu/peterb/0015-011/

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Stacks in Our Life
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More Stacks

• A stack is a LIFO structure Last In First Out

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Basic Operations with Stacks

• Push
• Add and item
• Overflow
• Pop
• Remove an item
• Underflow
• Stack Top
• Whats on the Top
• Could be empty

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Push

• Adds new data element to the top of the stack

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Pop

• Removes a data element from the top of the stack

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Stack Top

• Checks the top element. Stack is not changed

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Implementing Stack with Array

• Stack is stored as an array
• Max number of elements allocated

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Data Structure

• / Stack of integers intstack /
• struct intstack
• int stackAry / array of elem. /
• int count / N of elements /
• int stackMax / Max N /
• int top / index of top element /

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Create Stack

• static struct intstack createStack (int
  maxElements)
• struct intstack stack
• stack (struct intstack ) malloc(sizeof(struct
  intstack))
• if (stack NULL)
• return NULL
• / Head Allocated. Now initialize and allocate
  stack. /
• stack-gttop -1
• stack-gtcount 0
• stack-gtstackMax maxElements
• stack-gtstackAry (int ) malloc(maxElements
  sizeof(int))
• if(stack-gtstackAry NULL) / No mem. - free
  all /
• free(stack)
• return NULL
• return stack
• / createStack /

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Push

• static int pushStack(struct intstack stack, int
  dataIn)
• / full stack check /
• if (stack-gtcount stack-gtstackMax)
• return 0
• (stack-gtcount)
• (stack-gttop)
• stack-gtstackArystack-gttop dataIn
• return 1
• / pushStack /

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Pop

• static int popStack (struct intstack stack, int
  dataOutPtr)
• if (stack-gtcount 0) / empty stack /
• return 0
• else
• dataOutPtr stack-gtstackArystack-gttop
• (stack-gtcount)--
• (stack-gttop)--
• return 1
• / else /
• / popStack /

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Top

• / This function retrieves the data from the top
  of the
• stack without changing the stack.
• Pre stack is a pointer to the stack
• Post Returns 1 if success 0 if underflow
• dataPtr is a pointer to the data on the top
• /
• static int stackTop (struct intstack stack, int
  dataOutPtr)
• if (stack-gtcount gt 0)
• dataOutPtr stack-gtstackArystack-gttop
• return 1
• else
• return 0
• / stackTop /

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Empty?

• / This function determines if a stack is empty
• Pre stack is a pointer to the stack
• Post returns 1 if empty 0 if data are in the
  stack
• /
• static int emptyStack (struct intstack stack)
• return (stack-gtcount 0)
• / emptyStack /

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Full?

• / This function determines if a stack is full.
• Full is defined as heap full
• Pre stack is a pointer to a stack head node
• Post returns 1 if heap is full 0 if heap has
  room
• /
• static int fullStack (struct intstack stack)
• / Statements /
• return (stack-gtcount stack-gtstackMax)
• / fullStack /

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Driver Example 17.1 (1)

• include "StackIntAr.h"
• include ltstdio.hgt
• void main()
• struct intstack mystack
• int i
• int value
• mystack createStack(10)
• while(1)
• printf("Stack manipulation\n\n")
• printf("1. Push\n")
• printf("2. Pop\n")
• printf("3. Top\n")
• printf("4. End\n\n")
• scanf("d",i)

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Driver (2)

• if(i 1)
• printf("Value? ")
• scanf("d",value)
• if(pushStack(mystack, value))
• printf("Value d pushed in\n", value)
• else
• printf("Stack is Full\n")
• else if (i 2)
• if(popStack(mystack, value))
• printf("Value d popped\n", value)
• else
• printf("Stack is Empty\n")
• else if (i 3)
• if (stackTop(mystack, value))
• printf("Value on the top is d\n", value)
• else
• printf("Stack is Empty\n")
• else
• return

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Application Parenthesis matching