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A stack is a linear dynamic data structure that follows Last-In/First-Out (LIFO) principle. In a stack, addition of a new element and deletion of an element occurs at the same end which implies that the element which is added last in the stack will be the first to be removed from the stack.

Features of stack

  • It is a dynamic data structure.
  • It has dynamic size.
  • It uses dynamic memory allocation.

Operations of a stack

  • isEmpty(): Checks whether the stack is empty or not.
  • size(): Returns the size of the stack.
  • topElement(): Returns the top element of the stack.
  • push(x): Adds a new element ‘x’ at the top of the stack. Consequently, size of the stack increases by 1.
  • Stack Push
  • pop(): Deletes the top element of the stack. Consequently, size of the stack decreases by 1.
  • Stack Pop

Implementation of Stack

<?php
class CreateStack {
  public $top;
  public $stack = array();

  function __construct() {
    $this->top = -1;
  }

  // create a function to check whether 
  // the stack is empty or not  
  public function isEmpty() {
    if($this->top == -1) {
      echo "Stack is empty. \n";
    } else {
      echo "Stack is not empty. \n";
    }
  }

  //create a function to return size of the stack 
  public function size() { 
     return $this->top+1;
  }

  //create a function to add new element 
  public function push($x) {
    $this->stack[++$this->top] = $x;
    echo $x." is added into the stack. \n"; 
  }

  //create a function to delete top element   
  public function pop() {
    if($this->top < 0){
      echo "Stack is empty. \n";
    } else {
      $x = $this->stack[$this->top--];
      echo $x." is deleted from the stack. \n";
    }    
  }

  public function topElement() {
    if($this->top < 0) {
      echo "Stack is empty. \n";
    } else {
      return $this->stack[$this->top];
    }
  }
}

// test the code 
$MyStack = new CreateStack();
$MyStack->push(10);
$MyStack->push(20);
$MyStack->push(30);
$MyStack->push(40);

$MyStack->pop();
$MyStack->isEmpty();
?>

The above code will give the following output:

10 is added into the stack.
20 is added into the stack.
30 is added into the stack.
40 is added into the stack.
40 is deleted from the stack.
Stack is not empty.