Skip to main content

Data Structures: Introduction to Stacks

In the previous article, we saw how data is inserted and deleted in an array. In that case we could insert data at any place throughout the array. However, there are situations when we only need to add and retrieve data form the ends of the array. Stacks are one of the examples of this.

Stacks are data structures in which data could be added and retrieved only from one end (also known as the TOP of the stack). Suppose we insert 5, 6, 9 to the stack consecutively then while retrieving the first one to be retrieved will be 9 then 6 and then 5. That is why stacks are also known as Last-In-First-Out (or LIFO) structure.

A few terms regarding stacks:

  • Stack: Stack is a user-defined data structure. It is most commonly represented by linked-lists and arrays. In this article, we will be representing stacks with arrays.

  • Push: Adding data to the stack is known as pushing.

  • Pop: Retrieving data from the stack is known as popping.

Let us have look at this process with the help of an example. Suppose we have a stack represented by an array stack [10], which is empty to start with.


Now, stack [10] = 5


Now, stack [10] = 5, 10

pop() [It returns    10]

Now, stack [10] = 5

pop() [now it returns 5]

Now, stack [10] is again empty

In this way, a stack can grow and shrink over time.

Example Program

The process is quite simple so we straightaway move on to the example program in c++ that illustrates the implementation of stack.

In the following program, we have defined a class that has all the function implemented to represent a stack.

  // Example Program in C++
  // to illustrate Stacks

  // stack class
  class stack
   int arr[100];
   // 'top' will hold the
   // index number in the
   // array from which all
   // the pushing and popping
   // will be done
   int top;
   void push(int);
   int pop();
  // stack class definition ends

  // member functions
  // of the stack class
   // initialize the top
   // position

  void stack::push(int num)
    cout<<"\nStack Full!\n";


  int stack::pop()
    cout<<"\nStack Empty!\n";
    return NULL;

   return arr[top--];
  // member function definition ends

  void main(void)
   stack s;
   int ch;
   int num;

    cout<<"1> Push";
    cout<<"\n2> Pop";
    cout<<"\n3> Quit\n";


     case 1:
     cout<<"enter element:";


     case 2:
     cout<<"\n\nPopped: ";


Related Articles:

Popular posts from this blog

Fix For Toshiba Satellite "RTC Battery is Low" Error (with Pictures)

RTC Battery is Low Error on a Toshiba Satellite laptop "RTC Battery is Low..." An error message flashing while you try to boot your laptop is enough to panic many people. But worry not! "RTC Battery" stands for Real-Time Clock battery which almost all laptops and PCs have on their motherboard to power the clock and sometimes to also keep the CMOS settings from getting erased while the system is switched off.  It is not uncommon for these batteries to last for years before requiring a replacement as the clock consumes very less power. And contrary to what some people tell you - they are not rechargeable or getting charged while your computer or laptop is running. In this article, we'll learn everything about RTC batteries and how to fix the error on your Toshiba Satellite laptop. What is an RTC Battery? RTC or CMOS batteries are small coin-shaped lithium batteries with a 3-volts output. Most laptops use

The Best Way(s) to Comment out PHP/HTML Code

PHP supports various styles of comments. Please check the following example: <?php // Single line comment code (); # Single line Comment code2 (); /* Multi Line comment code(); The code inside doesn't run */ // /* This doesn NOT start a multi-line comment block /* Multi line comment block The following line still ends the multi-line comment block //*/ The " # " comment style, though, is rarely used. Do note, in the example, that anything (even a multi-block comment /* ) after a " // " or " # " is a comment, and /* */ around any single-line comment overrides it. This information will come in handy when we learn about some neat tricks next. Comment out PHP Code Blocks Check the following code <?php //* Toggle line if ( 1 ) {      // } else {      // } //*/ //* Toggle line if ( 2 ) {      // } else {      // } //*/ Now see how easy it is to toggle a part of PHP code by just removing or adding a single " / " from th

Generating XML Feeds (RSS, Atom) Using PHP

RSS/ATOM feeds are very common these days and almost all Content Management Systems (CMS) can generate it. But in the case when you want to generate it yourself or just want to learn how you can, read on! Both RSS and ATOM feeds are written in eXtensible Markup Language (XML) standard markup. Not just standard markups, you also need to be sure of what and how you put data in those markup elements (tags). For all this refer to the feed specifications of RSS and ATOM . XML itself is very strict and the standard specifications makes it even harder to generate valid feeds. And moreover, why re-invent the wheel when we can have it – ready-made. The solution I'm referring to here is, to use a third-party Library – Universal FeedWriter. FeedWriter is a PHP class written by Anis uddin Ahmad that can dramatically  ease-off feeds (both RSS and Atom) generation. You can download this library from  here . Every feed should have at least the following data: Feed title URL(of the webs