# Data Structure Questions and Answers-Stack using Array

## Data Structure Questions and Answers-Stack using Array

 Question 1
Which of the following real world scenarios would you associate with a stack data structure?
 A piling up of chairs one above the other B people standing in a line to be serviced at a counter C offer services based on the priority of the customer D all of the mentioned
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Question 1 Explanation:
Stack follows Last In First Out(LIFO) policy. Piling up of chairs one above the other is based on LIFO, people standing in a line is a queue and if the service is based on priority, then it can be associated with a priority queue.

 Question 2
What does the following function check for? (all necessary headers to be included and function is called from main)

 #define MAX 10 typedef struct stack { int top; 	int item[MAX]; }stack; int function(stack *s) { if(s->top == -1) 	 return 1; 	 else return 0; }
 A full stack B invalid index C empty stack D infinite stack
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Question 2 Explanation:
An empty stack is represented with the top-of-the-stack('top' in this case) to be equal to -1.

 Question 3
What does 'stack underflow' refer to?
 A accessing item from an undefined stack B adding items to a full stack C removing items from an empty stack D index out of bounds exception
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Question 3 Explanation:
Removing items from an empty stack is termed as stack underflow.

 Question 4
What is the output of the following program?

public class Stack { 	protected static final int CAPACITY = 100; 	protected int size, top = -1; 	protected Object stk[]; 	public Stack() 	{ 		stk = new Object[CAPACITY]; 	} 	public void push(Object item) 	{ 		if(size....of....stack==size) 		{ 			System.out.println("Stack overflow"); 				return; 		} 		else 		{ 			top++; 			stk[top]=item; 		} 	} 	public Object pop() 	{ 		if(top<0) 		{ 			return -999; 		} 		else 		{ 			Object ele=stk[top]; 			top--; 			size....of....stack--; 			return ele; 		} 	} } public class StackDemo { 	public static void main(String args[]) 	{ 		Stack myStack = new Stack(); 		myStack.push(10); 		Object element1 = myStack.pop(); 		Object element2 = myStack.pop(); 		System.out.println(element2); 	} }
 A stack is full B 20 C 0 D none of the mentioned
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Question 4 Explanation:
The first call to pop() returns 10, whereas the second call to pop() would result in stack underflow and the program returns -999.

 Question 5
What is the time complexity of pop() operation when the stack is implemented using an array?
 A O(1) B O(n) C O(logn) D O(nlogn)
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Question 5 Explanation:
pop() accesses only one end of the structure, and hence constant time.

There are 5 questions to complete.