#include <iostream>
#include <memory>
#include <vector>
#include <set>

// Observer from Observer design pattern
template<typename T>
class Observer {
 public:
  virtual void Notification(const T &event) = 0;
  virtual ~Observer() = default;
};

// Observable from Observer design pattern
template<typename T>
class Observable {
 public:
  void Notify(const T &event) {
    for (auto &observer : observers_) observer->Notification(event);
  }
  void Subscribe(Observer<T> &observer) { observers_.insert(&observer); }
  void Unsubscribe(Observer<T> &observer) { observers_.erase(&observer); }
 private:
  std::set<Observer<T>*> observers_;
};


// Pure Abstract / Interface class for service
class Service {
 public:
  virtual void Run() = 0;
  virtual ~Service() = default;
};

// Concrete class Foo
class FooService : public Service, public Observer<std::string> {
 public:
  void Run() override { 
    std::cout << "FooService running..." << std::endl; 
  }
  void Notification(const std::string &event) override {
    std::cout << "FooService received event: " << event << std::endl; 
  };
};

// Concrete class Bar
class BarService : public Service, public Observer<std::string> {
 public:
  void Run() override { 
    std::cout << "FooService running..." << std::endl; 
  }
  void Notification(const std::string &event) override {
    std::cout << "BarService received event: " << event << std::endl; 
  };
};

int main() 
{
    // Create a string-based event observable
    Observable<std::string> message_hub;
    
    // Container for services
    std::vector<std::unique_ptr<Service>> services;
    
    // Create services
    std::unique_ptr<FooService> foo_service = std::make_unique<FooService>();
    std::unique_ptr<BarService> bar_service = std::make_unique<BarService>();
    
    // Subscribe for events
    message_hub.Subscribe(*foo_service);
    message_hub.Subscribe(*bar_service);
    
    // Push services to container
    services.push_back(std::move(foo_service));
    services.push_back(std::move(bar_service));
    
    // Run the services
    for(auto &service : services) {
      service->Run();
    }
    
    // Push a notification
    message_hub.Notify("Services finished...");
    
    return 0;
}
by

C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}