Behavioral design patterns in C++ focus on the interaction and communication between objects, defining how they collaborate to achieve common tasks. These patterns emphasize the division of responsibilities between objects and provide solutions for organizing algorithms and relationships in a flexible and maintainable way.

1 Observer Pattern:

The Observer pattern establishes a one-to-many dependency between objects, where the subject (or observable) maintains a list of its dependents (observers) and notifies them of any state changes, usually by calling one of their methods.

Example:
Consider a scenario where you have a subject WeatherStation that keeps track of weather conditions and multiple observers such as Display, Logger, and Notifier that need to be updated whenever there's a change in the weather.

2 Strategy Pattern:

The Strategy pattern defines a family of algorithms, encapsulates each one, and makes them interchangeable. It allows the algorithm to vary independently from the clients that use it.

Example:
Imagine an application where you need to perform different sorting algorithms (e.g., Bubble Sort, Quick Sort, Merge Sort) based on different criteria. You can implement a SortStrategy interface and have concrete strategy classes implementing different sorting algorithms.

3 Command Pattern:

The Command pattern encapsulates a request as an object, thereby allowing for parameterization of clients with queues, requests, and operations. It decouples the sender of a request from its receiver, allowing for loose coupling between them.

Example:
Consider a remote control for a television. Each button press on the remote represents a command (e.g., turn on, turn off, increase volume, decrease volume). You can implement each command as an object (e.g., TurnOnCommand, TurnOffCommand) and store them in a queue to be executed when needed.

4 Iterator Pattern:

The Iterator pattern provides a way to access elements of an aggregate object sequentially without exposing its underlying representation. It abstracts the traversal of a collection, making it possible to iterate over different types of collections without exposing their internal structure.

Example:
Suppose you have a collection of books in a library. You can implement an iterator interface to iterate over the collection of books, regardless of whether it's implemented as an array, linked list, or any other data structure.