Instance variable

In object-oriented programming with classes, an instance variable is a variable defined in a class (i.e. a member variable), for which each instantiated object of the class has a separate copy, or instance. An instance variable has similarities with a class variable, but is non-static.
An instance variable is a variable which is declared in a class but outside of constructors, methods, or blocks. Instance variables are created when an object is instantiated, and are accessible to all the constructors, methods, or blocks in the class. Access modifiers can be given to the instance variable.
An instance variable is not a class variable although there are similarities. It is a type of class attribute (or class property, field, or data member). The same dichotomy between "instance" and "class" members applies to methods ("member functions") as well; a class may have both instance methods and class methods.
Each instance variable lives in memory for the life of the object it is owned by.
Variables are properties an object knows about itself. All instances of an object have their own copies of instance variables, even if the value is the same from one object to another. One object instance can change values of its instance variables without affecting all other instances. Instance variables can be used by all methods of a class unless the method is declared as static.
Example.
struct Request {
 static int count1; // variable name is not important
 int number;
 Request() {
 number = count1; // modifies the instance variable "this->number"
 ++count1; // modifies the class variable "Request::count1"
int Request::count1 = 0;
In this C++ example, the instance variable codice_1 is a copy of the class variable codice_2 where each instance constructed is assigned a sequential value of codice_3 before it is incremented. Since codice_4 is an instance variable, each codice_5 object contains its own distinct value; in contrast, there is only one object codice_2 available to all instances with the same value.