Stacks, Data Structure & Algorithms

Q. Explain what are the stacks? How can we use the stacks  to check whether an expression is correctly parentheses or not. For example (()) is well formed but (() or )()( is not well formed.

 

Ans:

The stack is a data structure that organizes data in a similar way one organizes a pile of coins. The new coin is all the time placed on the top and the oldest is on the bottom of the stack. When we are accessing coins, the last coin on the pile is the first coin which was removed from the stack. If we want to reach the third coin, we should remove the first two coins from the top of the stack first so that the third coin comes on the top of the stack and we can easily remove it. There is no way at all to remove a coin from anywhere other than the top of the stack.

A stack is useful whenever we need to store data and retrieve data in last in, first out order. Let us take an example the computer processes instructions using a stack in which the next instruction to execute is at the top of the stack.

To determine whether an expression is well parentheses or not:- the two conditions should be fulfilled while pushing an expression into a stack. At first, whenever an opening bracket is pushed inside a stack, there should be an occurrence a closing bracket before we reach the last symbol. Whenever a closing bracket is encountered, the top of the stack is popped until the opening bracket is popped out and discarded. If no such type of opening bracket is found and stack is made empty, then this means that the expression is not well parentheses designed.

An algorithm to check that whether an expression is correctly parenthized or not is written below:

flag=TRUE;

clear the stack;

Read a symbol from input string;

while not end of input string and flag do

{

if(symbol= '( ' or symbol= '[' or symbol = '{' )

push(symbol,stack);

else  if(symbol= ') ' or symbol= '[' or symbol =

'{' )

if stack is empty flag=false;

printf("More right parenthesis than left

parenthises");

else c=pop(stack);

match c and the input symbol; If not matched

{     flag=false;

printf("Mismatched

parenthesis");

}

Read the next input symbol;

}

if stack is empty then

printf("parentheses are balanced properly");

else

printf(" More number of left parentheses than right parentheses");

 

Posted Date: 7/10/2012 7:02:20 AM | Location : United States







Related Discussions:- Stacks, Assignment Help, Ask Question on Stacks, Get Answer, Expert's Help, Stacks Discussions

Write discussion on Stacks
Your posts are moderated
Related Questions
Open addressing The easiest way to resolve a collision is to start with the hash address and do a sequential search by the table for an empty location.

how to convert 12 hour format into 24 hour format using c program

Determine about the Post conditions assertion A  post condition is an assertion which should be true at completion of an operation. For instance, a post condition of the squ

What are the structures used in file-system implementation? Several on-disk and in-memory structures are used to execute a file system a. On-disk structure include P

What do you understand by term structured programming? Explain the structured programming as well.                                 Ans. S tructured Programming is expla

I need to know about data structure and algorithms. can you help me?

reverse the order of elements on a stack S using two additional stacks using one additional stack

Abstract data type The thing which makes an abstract data type abstract is that its carrier set and its operations are mathematical entities, like geometric objects or numbers;

Z-Buffer Algorithm Also known as the Depth-Buffer algorithm, this image-space method simply selects for  display the polygon or portion of a polygon that is nearest to the view

How sparse matrix stored in the memory of a computer?