understanding ArrayList

Divyansh Pratap Singh — Fri, 02 Sep 2022 00:39:06 +0000

Understanding the concept of ArrayList :

Authors : Divyansh Pratap Singh (twitter)

Array List vs Array :

Array List	Array
they have variable size	they have fixed size
they have non-continous memory allocation	they have continous memory allocation
they can store only objects	they can store primitive data-types ex. int , float

Implementing ArrayList

    `import java.util.ArrayList;
    public class arrayy_list{
        public static void main(String[]args){

            ArrayList<Integer> list = new ArrayList<Integer>();

        }
    }
   `

Similarly for declaring String

ArrayList<String> name = new ArrayList<String>();

Adding element in ArrayList

we use add function to add an element in ArrayList

ArrayList<Integer> list = new ArrayList<Integer>(); list.add(3);

Adding elements 3,2,5,0 --> below is the complete code for adding element
'''
import java.util.ArrayList;
public class arrayy_list{
public static void main(String[]args){

            ArrayList<Integer> list = new ArrayList<Integer>();

            list.add(3);
            list.add(2);
            list.add(5);
            list.add(0);
        }
    }

Accessing elements of ArrayList :

to access element in ArrayList we use get function . Inside get function we pass the index position of the element .

list.get(0);

Gives us : 3

Adding element in middle of ArrayList :

add function adds an element at the end of the ArrayList ; to add element at any position in ArrayList we use add function and pass 2 parameters ;

list.add(<indexposition><element>);

list.add(0,9);

Result : [9,3,2,5,0]

Changing element in ArrayList :

to change a value in ArrayList we use set function . The function takes 2 parameters ; 1st is the index position of the element you want to change and the 2nd parameter is the new element.

list.set(0,8);

Result : [8,3,2,5,0]

removing an element from ArrayList :

to remove a element from ArrayList we use remove function and pass the element index position as the parameter.

list.remove(0);

Result : [3,2,5,0]

printing complete ArrayList

System.out.println(<ArrayList name >); System.out.println(list);

Result : [3,2,5,0]

finding size of Array in C

Divyansh Pratap Singh — Wed, 31 Aug 2022 13:16:45 +0000

What we will learn ?

In this read you are going to learn how to find the size of the array in C programming language and the concepts behind its working .

Introduction :

As in any other programming language like Java we have length property of array through which we can easily find out the size or the length of the array but in c arrays do not have any such properties through which we can easily find out the size of the array . Though there are two ways through which we can find out the length or size of the array in our C programming language ; but in comparison to other languages like of java it's a bit complicated . So , in this blog you are going to learn how to find the size along with the working and the reason why it is happening so .

Method 1

Using a constant variable size

So , we will be defining an constant variable 'Size' which would store the size or the length of the array . Suppose we have to store five values in our array so the value of our size variable is 5 .

const  int Size  = 5 ;

Here , in the above line const is a keyword that declares the variable Size as constant i.e we cannot change the value of Size in the upcoming program .

Now , the next step is to define and initialize our array.

 int arr[Size] = { 1 , 2 , 3 , 4, 5};

here ; in the above line we declared an array of name 'arr' and passed the values inside the array ; also do remember to pass the size of the array .

code of c program to print the elements of Array :

#include<stdio.h>
#include<conio.h>
void main(){
clrscr();

const int size = 4;
int arr[size] = {1,2,3,4};

for(int i = 0 ;i<size ;i++){
printf("%d \n " , arr[i]);
}
getch(); }

Additional info :

Case 1 :

 const  int  size = 4;
  int arr[size] = { 1,2,3 };

In this code we have set the size of the array as 3 and inside the array we are only passing 3 values . Will we get an Error ?

No , actually what happens when we declared size as 4 then there are 4 blocks created where you are only entering values in 3 blocks so , the last block remains empty . So , the empty block is filled by 0 by default during the run time ._

Case 2 :

  const  int  size  = 2 ;
int arr[size] = {1,2,3};

here , in the above code we have set our size as 2 so now we have 2 blocks and later in the program we are storing 3 values ; we have 2 blocks and we are storing 3 values so this is going to throw us an error ._

Method 2

Using sizeof operator

So , In the above section we have learnt how to find out the size of array using a constant variable and now in this section we are going to find out the size or length using sizeof operator .

So , before jumping in to the implementation part first let's us understand what is sizeof operator .

The sizeof is an unary operator in c and c++ . It is basically used to compute the size of the operand .The result of sizeof operator is an unsigned integral type which is denoted by size_t .
sizeof operand can be used with any data type , primitive data type example int , float as well as compound data type example Structures .

Usage

when sizeof() is used with datatypes like int or float then it returns the memory occupied by them .

printf("%lu" , sizeof(int));

this would give 4 as an output

when sizeof() is used with an expression then it would return the size of the expression .

float  a = 1.2;
double b = 1.0;
printf("%lu" , sizeof(a+b));

this would give 8 as an output.

Returning back to our Question :

 int arr = [1,2,3,4];

here in the above code i had declared and initialized an array and now i want to print the size of the array , so let's find out the size using sizeof() operator .
So , for better understanding i am storing the size in a variable named size , if you wish then you can directly print the size .

int arr[] = {1,2,3,4,5};
int size = sizeof(arr) / sizeof(arr[0]);

Now , you might be wondering why i had divided the sizeof(arr) with sizeof(arr[0]) , let me explain .

sizeof(arr) operator will give you the total memory occupied by the array arr and similarly sizeof(arr[0]) will return you the memory occupied by the single element so by dividing the total space by the space ocupied by 1 element then we will get the number of elements .

You can understand this way , suppose a guy paid 50 INR in total for buying chocolates , now you are told that 1 chocolate was for 10 INR and now tell me the number of chocolates the guy bought .
(40/10) which is 4 chocolates . This very same concept we are using there in sizeof().

Important : sizeof operator do not returns size it returns the memory occupied by the operand .

Entire code for printing the size of Array using sizeof operator.

#include<stdio.h>
#include<conio.h>

void main(){
clrscr();
int arr[] = {1,2,3,4,5};

int size = sizeof(arr) / sizeof(arr[0]);

printf("%d" , size);
getch()  };

Thankyou , for giving it a read I hope you understood the concept and if you have any doubt please comment below .

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