// This Article is contributed by Debarup Sarkar
Declaring a variable :

Whenever we will declare a variable, we should always know what type of value it should hold, whether it’s an integer (int), decimal number (float / double), character value (char).

In general, the variable is declared as follows :

Datatype variableName = VALUE;

● int : Integer value
● float, double : Decimal number
● char : Character values (including special characters)
● bool : Boolean values (true or false)
● long : Contains integer values but with larger size
● short : Contains integer values but with smaller size

Table for datatype and its size in C++:

(This can vary from compiler to compiler and system to system depending on the version you are using)

Datatype & their default size :

A) int — — 4 bytes
B) char — — 1 byte
C) short — — 2 bytes
D) bool — — 1 byte
E) long — — 8 bytes
F) float — — 4 bytes
G) double — — 8 bytes

Example: To declare an integer variable ‘n’ with a value of 6, the structure looks like: int n = 6; & Similarly, this way other types of variables can also be declared

Some Rules For Variable Names :

● Can’t begin with a number.
● Spaces and special characters except underscore( _ ) are not allowed.
● C++ keywords (reserved words) must not be used as a variable name.
● C++ is case-sensitive, meaning a variable with name ‘A’ is different from variable with name ‘a’. (Difference in the upper-case and lower-case holds true)

Printing/Providing output:

For printing statements in C++ programs, we use the ‘cout’ statement .
For example: If you want to print “Hello World!” (without parenthesis) in your code, we will write it in following way:

cout << “Hello World!”;

Full Code :

#include <iostream>
using namespace std;

int main() {
cout<<”Hello World!” ;
} 

Output: Hello World!

Line separator:

For separating different lines in C++, we use endl or ‘\n’ .

code example :

#include <iostream>
using namespace std;

int main() {
cout<<"Hello World(1)”<<endl;
cout<<"Hello World(2)”<<’\n’;
} 

Output:
Hello World(1)
Hello World(2)

Taking input from the user:

To take input from the user, we use the ‘cin’ statement.
For example: Taking Number Input from user :

int n;
cin >> n;

Lets try to code this : User wants to take input of 2 numbers and then print the sum of them:
Code:

#include <iostream>
using namespace std; 

int main() {
int a, b, sum;    // declaring data types & variables 
cin >> a;
        // taking input from user
cin >> b;       //  taking input from user
sum = a + b;    // calculation 
cout << “Sum of two numbers: ”;  // printing output 
cout << sum << endl;             // printing output 
}

// Input & Output discussion : 
   /* Input :
        3
        5
     Output : 
        Sum of two numbers: 8   */

Operators in C++
There are 3 types of operators in C++
● Arithmetic operators
● Relational operators
● Logical operators

1) Arithmetic operators:
These are used in mathematical operations in the same way as that in algebra

OPERATOR	DESCRIPTION
+	Add two operators
–	Subtracts second operand from the first
*	Multiplies two operands
/	Divides numerator by denominator
%	Calculates Remainder of division

2) Relational operators:

C++ relational operators specify the relation between two variables by comparing them.
Following table shows the relational operators that are supported by C++

OPERATOR	DESCRIPTION
==	Checks if two operands are equal
!=	Checks if two operands are not equal
>	Checks if operand on the left is greater than operand on the right
<	Checks if operand on the left is lesser than operand on the right
>=	Checks if operand on the left is greater than or equal to operand on the right
<=	Checks if operand on the left is lesser than or equal to operand on the right

Logical operators:

OPERATOR	DESCRIPTION
&&	Logical AND
| |	Logical OR
!	Logical NOT