Understanding Arrays in Programming: Declaration, Initialization, and Memory Representation

video we will see what is the need of array, what is array, types of array, how arrays can be declared, how arrays

can be initialized and how data is to be represented in memory or you can see the memory representation of an array. Fine.

See, I guess you are aware with the fundamental data types that is int, float, care, double etc. And if I write

like this int a is equal to five. It means you have declared one variable variable name is a type of the data type

of this variable is int and the value stored in this variable is five. Fine. This is one variable variable

declaration you can say. Now how this value is to be stored in memory. Let us check. So let us take this is our main

memory. You can uh draw it vertically also. Fine. So see these are bytes. So you can say memory is a long tape of

bytes. You can say bite means eight bits. This is one bite. This is one bite. This is one bite like this. So

this can be extended to this side and this side also. That is why I'm taking open end. So now how this variable can

be stored here. When the compiler compile this line then what happens? The what memory manager will do? memory

manager will allocate some space for this variable to store this value five here how much space would be allocated

see the data type int how many bytes it will take four bytes in typical compilers to store an integer data type

it will take four bytes in traditional compilers we consider it two bytes so you can say two or four it's up to you

generally we take four bytes that is why I'm taking for storing one integer it will take four bytes Fine. So we have

only one integer. That is why how much memory would be allocated? Four bytes would be allocated. Four bytes. Fine. It

means how many bits? 8 into 4 that is 32 bits because one by one by is equal to 8 bits.

Fine. Now how this data is to be stored? First of all, this decimal number five is to be converted into binary digits,

binary numbers. Sorry. That is in 32 bits. How? In 32 bits this number can be represented like this.

29 zeros would be there and then we will write 1 0 1. Now this binary this binary number is to be stored in memory. Now

how this data is to be stored. This four bytes is to be allocated 1 2 3 4. Let us suppose these four bytes are to be

allocated to store this five like this. these four bytes. So these four bytes are this is a closer

look here. We are going to store these digits like this and 1 0 1 at the end. 8 bits here 8 bits. 8

bits 8 bits that is 32 bits. This is how the number is going to be stored in memory. Fine. And suppose at address you

can say see address is always in hexadesimal form. But here for simplicity purpose I'm taking let us

suppose the address is address of this bite is 100. Let us suppose so address of this

bite would be 101 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 102

and 103. So it's 100 1 1023. These four bytes to be used to store the

center. See this address would be in hexadimal form always. It's not like 100 or thousand or something like this.

Hexad decimal means always hexadimal would be represented by prefix with the 0x. Then you can say 677

or C and zero something like this. In this form the address would be there but here I'm taking just 100 for simplicity

purpose. So now we'll discuss what is need of array. See in this variable we can store only one value at a time. If I

want to store six then what would happen? I will write here six and five is overritten. Five is no more

now. Fine. If I want to store seven then I'll write seven. And now five and six are no more. And here you will insert

seven or you can say overwritten those five and six. So at one time you can store only one value. If I want to store

more than one value. Suppose in my class I have 60 students and I want to store all numbers of all

the 60 students. Now what would happen? You have to take in this case if you follow this approach in that case you

will have to take 60 variables because one variable can only store only one value at a time. See because we have to

process large amount of data. That is why the concept of array came. Now you will modify this declaration such that

under one variable name we can store ro numbers of all 60 students. That is what array. Now how you can do

this? See same data type would be there. Here we have name but rather than storing one value now I want to store 60

values. Now obviously you have to tell the compiler that I want to store 60 values. Then you have to give the size

of your array. So here like this we are going to give the size. Fine. So this is what you can say the

declaration of array. General syntax would be what? Data type. Then array name. Array name is a then in brackets

size of the array. And here you will write what? Constant value. Okay. See this is invalid declaration.

If you write int a this this is invalid declaration. You cannot leave it blank. This is also

invalid declaration. If you write int a and here you write size is n sorry int n and here you here you write n this is

also invalid declaration here you have to write what constant you can write here a variable but in that case for

that case you have to declare macros before main function and below that header files you will declare one macro

you can say hash define variable name n size is 100 in that case after that in main function You can write int a and in

breakers you can write that variable name fine that is different logic but simply you cannot declare something like

this you have to declare this data type then array name then size should be constant now see this declaration of

array is language specific I am here considering the syntax in C language in Python maybe it's different in Pascal in

uh you can say that for language the declaration syntax would be a little bit different So it is language specific.

Fine. Now this is what the array declaration. Now see this is declaration of 1D array. Types of array. Types of

array. Three types of arrays are there. 1D array. One-dimensional, two-dimensional and multi-dimensional

array. So in this video I'm going to talk about 1D array. So this is declaration of 1D array. So in this we

are having one row with 60 columns, 60 values in columns. Fine. Now see how the arrays can be initialized and after that

we will discuss how the arrays can be represented in memory. So see how you can define an array. What is definition

of array? You can say that array is a collection of more than one data items or more than one elements. But condition

is what? The data type of those element should be same or you can say collection of the more than one data items of same

data type. See here five we can store five elements in the array but all the five elements should be of integer type.

Let us take this example. See this is a valid array because here the size of array is 1 2 3 4 5 elements are there

but all the five elements are of same data type that is integer. Here all the data items are of same data type that is

character. You can also declare a character array like this. Data type should be character. Suppose name of

array is a or b you can take and size is suppose 10 that is also fine you can take float array also like this float

array name is suppose b and I'm taking size is five so that is also fine but see this is fine this is fine because

all in this in this array all the elements are character type same type but this is not valid this is not valid

because in this array 1 2 3 4 5 size is five But here we have integer value also and character value also. So different

data types items are there. That is not possible in array. All the data items should be of same

data type. Now how the data how the elements of the arrays are stored in this memory? All the elements are stored

in consecutive locations or you can say continuous locations one after another. How the data is to be stored in the

memory I'll discuss in this video only. That is very important point. Fine. All the elements are stored in consecutive

locations and index would be started from zero. Although somewhere we can start the index from one that is also

fine. But generally we take the index of array should be started from zero. Now how to access those elements of the

array? We will also discuss that thing. Fine. See now how the array is to be initialized. Arrays can be initialized

by two types. One is at compile time and one is at runtime. Compile time means static initialization would be there at

the time of declaration only. At the time of declaration only you will specify what what elements you want in

the array and at runtime means while executing the program at the runtime you can ask from the user what are the

elements of the array. Fine. Now one more important point about array is that that it is a fixed size array. Now we

have declared size of array that is five. Now at runtime you cannot change the size of the array. It's not like you

can store six elements. Fine. You can store only five element maximum. You can store two elements that is fine but you

cannot exceed from this limit. This is fixed. Now this is maybe you can say a drawback of array that you cannot change

the size of the array during runtime. Although one concept is there that is of dynamic array but we will discuss those

things in later what is dynamic array what is ling list something like this in this video I'm discussing only in the

fundamentals of array so now we'll see how array can be initialized at compile time first of all see at the time of

declaration only you will specify the elements of the array suppose five elements I want so I can specify here

these Five elements, fine. So that is fixed. These five elements would be stored in the array. This is compile

time initialization. Here the size is five. So you cannot write here six elements. If you write

six, seven or more than five elements then it will give a compile time error. You cannot exceed from this limit.

Although you can specify less than five elements. If I specify here only six and two that is also fine. remaining for

remaining four position it will store what zero it will initialize with zero but more than five you cannot write

here. So this is uh compile time initialization now how these this these elements has to be stored in this

memory. Let us check see now the size is to be allocated is 5 into 4 that is 20 bytes. Memory manager will allocate 20

bytes but in consecutive bytes consecutive bytes should be allocated. Let us suppose it he will allocate from

this address and let us suppose address I'm taking 100. So till 100 to 109 here the data is the memory memory is to be

allocated to these elements. Now how the data is to be stored first of all the six six is to be converted into binary

form and then the data is to be stored here. Six is to be stored here.

Six in these four bytes. Next two would be stored. So this is how this data is to be stored. See first of all this is

to be converted into binary form. Fine. But I'm not taking here binary form. I'm just simply writing six in these four

bytes in these four bytes two then four then three and zero. See this 6 2 4 3 and 0. These are in consecutive

locations continuous locations. So for simplicity purpose I'm going to represent this data like this. Fine.

This block is having these four bits. This is also having sorry four bytes. This is also having four bytes that is

32 bits. But for simplicity purpose I'm writing here like this. So this is our array name is a and address of this is

100 100. So now address of this two. This address of two would be what? See this

two would be 1 0 4. This would be 1 0 8. This would be 1 1 2 and this would be 11 1 6. And why so? Because this this

element is going to take four bytes. 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10

1 10 1 10 1 10 1 10 1 0 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 10 1 02 and 103. That is why it is 104. How this

address is to be calculated? What is the formula? The formula is before going to formula let us check the

this this index would be 0 1 2 3 4 we are going to start the index of this array with zero for simplicity purpose

somewhere it is also started with one that is fine but here I'm going to start with zero so now how the data is to be

accessed how you can calculate this address so this is how you can write at a of a of zero at index zero we have six

a of 1 We have two, a of two, we have four, something like this. Fine. How to access how to access the data? How to

calculate the address? See, we know the base address of the array. Base address means from where the array is to be

started. Array is to be started from 100. So, base address is 100. So, how does this address to be calculated?

Suppose I value is I would be starting from 0 till 4 means 0 to n minus 1 or you can say size of array. N is equal to

size of array. Right? So if you want to access I equ= 2 this data when I is equal to 2 means I=

2 that is third value. How to access this value? So the formula would be base address plus this I value into size of

data type you have taken the data type of array is here int. So size would be four bytes. Now how to calculate address

for this location I is equal to 2. See base address is 100. So these address would be in hexadimal form. Just to make

you understand I'm taking here integer form. 100 plus I value is two. You want to calculate address for this two into

size of data type. Data type is in size would be four bytes. So now here you will take 100 + 8 that is 10

8. The location would be 108 where this value is there. The data is to be there. So that is why a of 2 a of 2. A of two

is what? Four. That is this is how you can after finding the address you can access the data. Fine. So see see the

array follows the random access. You can access any data with a constant time. If you know the base address because if

you know the base address you just simply need to do only one plus and one into uh one you can say addition and one

multiplication and you can access the data. So the time taken for this accessing is order of one that is

constant time and array follows what random access method. If you and let us suppose if you take character array here

we have cap and array name is B and I'm taking here size is 10 and here I'm initializing this character array also

and I'm taking some values fine. So now how these values to be stored? See I have taken size as 10. So in memory how

many bytes is to be allocated. So for this size of character is character will take one byte. 1 into size is 10. Here

we have 10 characters. So 10 bytes would be allocated. Fine. Somewhere 10 bytes should be consecutive. Let us suppose

this is also there. And after maybe not 119 but from here from here

from 122 10 bytes till 132 has been allocated to this character array B. So how the data

is to be stored here? Here the space is to be allocated. Now this this data is to be stored here.

But here we have null because we have specified only 1 2 3 4 5 characters but the size has been

allocated to for 10 characters. So this is now you can say that wastage of space. So now see the drawback you can

say the one another drawback of this array is what you have to specify the size at compile time but in advance we

don't know how much space we needed. Maybe sometimes you have declared that I want an array of size 100. So now that

100 the space of that 100 uh elements or you can say 400 bytes has been allocated to you for this array name a but

actually you are using only you are storing only 10 integers. So you are wasting that space now. So that is

drawback of that that array that static declaration of array and sometimes you want to store more data than you have

declared here. Now suppose you have declared the size of array is 100 for 100 integers but now actually when

runtime you want to store 200 integers but that is impossible because you have already declared the size. Now if you

ask to the memory manager that I want to store 200 integers so I want to extend my array. So now what memory manager

will do? Memory manager will allocate you a space of fresh new space of for 200 integer. So you can say 800 bytes in

consecutive locations. And what memory manager will do? Memory manager will copy the data because previously he has

allocated space for 100 integers to you. So those 100 integers would be copied from there to the new location. Fine. So

that would be very tedious work to do. So this is how you can initialize the array at compile time only. Now at

runtime how to initialize? So at runtime you can initialize the array using loops maybe for loop while loop do loop and

some predefined function standard functions that is scanf. I'm going to write down that code here. See let us

suppose I have I have declared an array of size five fine now at runtime I want to ask from the user which data he wants

in this array. So now what I'll do see printer function is for what? For printing something on the screen. So so

I I'm writing here enter the elements of array. So this line is to be printed on your

screen. Now for taking the input from the user you will write what scanf

but first uh the most important point about this is you have to use some loops because you are going to take

continuously five inteious from the uh user. So we'll suppose I'm taking for loop here in I I would be started index

would be started from zero I less than size minus one that is four and I ++. So within this for loop you can write

percentage D and array name A. So this is how uh during runtime you can take that uh value from the array. I'm going

to discuss it how the data is to be taken from the user. How the data is to be stored in the array in next video. So

these are some points that we have discussed in this video. See array is a fixed size. Fixed size means once you

have declared the size at compile time, you cannot change it at runtime. Fixed size sequenced collection of data items

of same data type. Data items should be of same data type. That is also a drawback of the array. Fine. To access a

particular element in the array what you will have to write just write array name and in the brackets you will write the

index value. Suppose you want to access the first element then you will write what array and in bracket you will write

zero because we are going to start the index from zero. Data items are stored in continuous locations and random

accesses. There you can access any elements and that will take a constant time order of n. How you are going to

access that? I have discussed with the help of formula. Types of area three, 1D, 2D and multi-dimensional array. We

have discussed how 1D array. So this topic we have discussed declaration, initialization, accessing of this 1D

array. In next video we are going to discuss how the data is to be inserted, how the array is to be traversed,

different types of operations on 1D array. first of all with their time taken and after that we will discuss

what is 2D array as well as how the data is to be accessed from 2D array fine so I'll see you in the next video till then

bye-bye take