C++ is a strongly typed language because every variable must be declared with a data type.This variable cannot be later assigned a value of another data type.For example,if we declare an integer called int abc then, abc can only store integers.It cannot store any float values.
A C++ identifier is a name used to identify a variable, function, class,object or any other user-defined item.Variables are identifiers that the user defines or creates to store values.
A variable is essentially a named memory location.It is ‘named’ because the user gives a name according to his own discretion and a variable is nothing but a storage or a ‘memory location’ where data is stored.
A variable must be initialised with a data type.Initialising a variable is demonstrated by the following command:
- int a = 7;

Certain rules before choosing identifier names(or variable names) are as follows:

C++ is a case-sensitive language. That means that identifiers such as value,Value,VaLue are all different identifiers.
Identifiers can only contain letters , digits, and the underscore character.
An identifier can be started only with a letter or an underscore character. You cannot start the identifier with a digit.
C++ has a set of reserved keywords that cannot be used as identifiers.

Constants

A constant expression is a named memory location for a value. A constant expression cannot have its value changed in the program during run time.
C++ uses the keyword ‘const’ to indicate that an expression is a constant.
When a constant is declared in C++, you must assign a literal value to that constant at the same time. This cannot be assigned later or changed later in the code.