Question

1. Name three types of data structures.
2. How is an element in an array different from an element in a record?
3. How is an element in an array different from an element in a linked list?
4. Why should we use indexes rather than subscripts to identify array elements?
5. How are the elements of an array stored in memory?

Answer 1

What is a Data Structure?

Data Structure, the name itself suggests us that organizing data in a particular structure. In other words Data Structure is used to store or organize data in a specified fashion. For example Array is one of the Data Structures which is used to store similar type of data (In an Integer Array we can store only Integers not other data types like Strings etc.) in a continuous memory locations (First we need to specify size of an Array, based on Array size required memory will be allocated to that array in the RAM and as and when we put data in that Array based on index data will be stored in the one of the indexes in allocated memory).

Name three types of data structures.

We have so many Data Structures.

All the Data Structures are categorized in two categories

1. Linear

2. Non-linear

1. Linear Data Structures

As I mentioned earlier there are so many Data Structures let's list a few here

Array

Stack

Queue

Linked List

2. Non-Linear Data Structures

Let's list a few Non-Linear Data Structures here

Tree

Graph

How is an element in an array different from an element in a record?

The difference between Array and Record is, Array stores data of same type(only int or only string etc.) in contiguous memory locations where as Record is also a Data Structure which stores data of multiple data types (you can store int, string, float etc. in single record) in fields. A record is used to stored data of different data types. You can consider an example as Database record. If you take Student table, in single record we store name of type string, we store age of type int, we stored data of birth of type date etc. Basically both the Data Structures are different each other.

How is an element in an array different from an element in a linked list?

The main difference between Array and Linked List is, in the case of Array data will be stored in contiguous memory locations where as in the case of Linked List data will be stored where ever memory is available to store an element.

For example if we want to Store 10 elements in the memory by using Array Data Structure then we need contiguous memory if we don't have we can't store using Array. For Linked List we don't need to have contiguous memory location but If we have memory at 10 different locations to hold our 10 elements that is fine, we can use Lined List to store 10 elements at different memory locations but we can't use Array.

Coming to our question, as discussed above there is a lot of difference between Array and Linked List in terms of storing data (element) and organizing data (element).

Why should we use indexes rather than subscripts to identify array elements?

First of all both index and subscript are used to access an element from an Array.

Subscript actually represents position of the element(2nd element or 3rd element etc.) with in the array where as index represents displacement value from the beginning of the array.

For example to access an element at position 3 we write something like below

numbers[3]

here 3 is the subscript, which says want to access 3rd element.

In the case of index, numbers[3]

here 3 is subscript but internally it uses index approach so it calculates displacement value from the beginning of the array to fetch an element at the position 3.

displacement value = array starting address + subscript * size of data type (This formula gives you at which address location our element exist)

How are the elements of an array stored in memory?

Elements in an Array will be stored in a continuous memory locations. What does that mean?

Let's understand.

I want to create an Array with size 10. Which means I want to create an Array which will store 10 elements of type Integer.

Let me create example Array in Java (you don't need to have knowledge on java to understand below statement. If you don't understand let's not focus on below statement but understand that we want to create an Array with size 10 elements of type int)

int[] numbers = new int[10];

The above java statement says to the java program executor that create an Array with size 10 and type of the data that stores is Integers.

In Java to store int data type it takes 4 bytes of memory.

Let's consider our memory starting address is 2000. Each memory location will have an address.

20	22	27	18	15	17	10	15	11	10
2000	2004	2008	2012	2016	2020	2024	2028	2032	2036
0	1	2	3	4	5	6	7	8	9

First row represents our Array with data.

Second row represents our Array addresses for each index.

Third row represents our Array indexes.

When you ask array give me data which is in index five. Array index starts with 0.

numbers[5]

address of 5th location = starting address + index * size of data type (in our case int 4 bytes) = 2000 + 5 * 4 = 2020

numbers[5] will return us 17 that is the data which is in the array index 5.

You may have a question about starting address that how do I know starting address, you don't need to worry about it that will be taken care by the program executor. I am explaining here how internals work.