Variables and Data Types

Ok lets learn the two very important concepts in C programming , variables and data types. 

So as the name suggest variable is something that is not constant that varies , we use variable in programming to store data , that could be numbers or text and data type defines the type of the data stored in the variable , so let me give an example to make it easy

Lets sat we want to store someone phone number in a program and display the number , so where we are going to store the number , we store it in a variable named “phone” (variable names are user defined , we give names to the variable , but there are some rules to follow , which I will explain very shortly)

So this would look like

Phone = value ;

Here value can be any integer

So this becomes

Phone = 123456;

This implies that phone is a variable to which we have assigned a value 123456

Now we also have to tell the compiler that “phone” can store what kind of value , like an integer or a character or a decimal value and so on and we tell this by using data type which tells the compiler  what is the type of data the variable can store , there are different key word for different data type and the major types are

int for integer value

char for storing individual characters

float for decimal value

double same as float but can store larger numbers  

please note that every data type has predefined range within which we can store values which we would discuss shortly

So to use a variable we write

int phone = 123456;

technically speaking variables are named piece of memory that we can assign a value , if you find that difficult , consider variables as a kind of box that we use to store data , the label of the box is its name and the type of content inside the box is its data type and the content is the value

Some rules to follow while naming a variable are as follows

1 > no two variables should have the same name in other words variables should be unique

2> variables name cannot begin with a number for example 123baby

3> variables can only have a to z , A to Z , 0 to 9 and underscore in it

4> variable have to be declared before they are used that means to specify the data type ,

 Syntax for variable declaration is

Data type variable_name = value_of_varibale ;

let’s find more about the integer data type

Data Type	Byte	Range
int	4	–2,147,483,648 to 2,147,483,647

In the above table the byte field represents the maximum size of a number an integer data type can hold and range displays that the number could be between negative 2,147,483,648 to positive 2,147,483,647 , so how we are getting this value ,
 well for information every data type has a certain range but to understand the relation between byte size and range let us do some binary calculation

So computer stores everything in bits that is zero or one , now 4 byte is equal to how many bits , 

since 8 bit is 1 byte so 4 byte will be 32 bit

8 bit = 1Byte

4Byte = 8 * 4 = 32 bit

So in binary if we have 32 numbers of 1s then the value in decimal form will be 4,294,967,295 but since int can store both negative and positive value this number splits in two equal parts including 0 , so the range splits in half to  –2,147,483,648 to 2,147,483,647  , but if we add these two values we would get 4,294,967,295 , this is how we get the  range from size , if possible try to find the other range by yourself ,
This link might be helpful to you Microsoft library

Enough with variables and data types now let us do a program with variable

 main()

{

int phone = 123456;    

 printf("Hello World \n");

printf("Your phone number is %d \n",phone);

getch();         

 }

This program display hello world followed by 123456

Now let us examine the new elements in the program 

int phone = 123456;   well this is not new , here we have declared a variable with integer type and assigned a value to it

printf("Your phone number is %d \n",phone);  printf is explained before , 
in order to display the variable in the statement we use the %d notation inside the quotes then a comma and then the variable name, 
please remember that the position of %d in the statement will decide the position of the variable in the statement , so it %d is before the word number then the variable will appear in that position

Now let us do a program with more numbers of variables

main()

{

int phone = 123456;    

int mobile = 9876543;

printf("Hello World \n");

printf("Your phone number is %d and mobile is %d \n",phone,mobile);

getch();         

 }

This is how we express multiple variable in a statement , here the first %d is for phone and the second for mobile variable

Some examples of how to declare and display other data type are

main()

{

float number = 55.5;    

printf("value of number is %f”,number);

getch();         

 }

 main()

{

double number = 44.54;    

printf("value of number is %lf”,number);

getch();         

 }

main()

{

Char car = ‘m’;

printf("value of character is %c”,car);

getch();         

 }

As we can see we have %f is for floats , %lf is for double and %c is for character