static variables in cpp code example

Example 1: static variable in c++

/*
this example show where and how
static variables are used
*/

#include <iostream>
#include <string>

//doing "using namespace std" is generally a bad practice, this is an exception
using namespace std;

class Player
{
  int health = 200;
  string name = "Name";
  
  //static keyword
   static int count = 0;
public:
  //constructor
  Player(string set_name)
    :name{set_name}
  {
    count++;
  }
  
  //destructor
  ~Player()
  {
    count--;
  }
  
  int how_many_player_are_there()
  {
    return count;
  }
  
};

int main()
{
  Player* a = new Player("some name");
  cout << "Player count: " << *a.how_many_player_are_there() << std::endl;
  
  Player* b = new Player("some name");
  cout << "Player count: " << *a.how_many_player_are_there() << std::endl;
  
  delete a;
  
  cout << "Player count: " << *b.how_many_player_are_there() << std::endl;
}

/*output:
1
2
1
*/

Example 2: static inside local scope in c++

#include<iostream>
//Singleton class is a class having only one instance
class SingleTon {

public:
	static SingleTon& Get() {
		static SingleTon s_Instance;
		return s_Instance;
	}//there is only one instance of static functions and variables across all instances of class
	void Hellow() {}
};
void Increment() {
	int i = 0;//The life time of variable is limited to the function scope
	i++;
	std::cout << i << std::endl;
};//This will increment i to one and when it will reach the end bracket the lifetime of var will get  destroyed
void IncrementStaticVar() {
	static int i = 0;//The life time of this var is = to program
	i++;
	std::cout << i << std::endl;
}//This will increment i till the program ends
int main() {
	
	Increment();//output 1
	Increment();//output 1
	Increment();//output 1
	IncrementStaticVar();// output 2
	IncrementStaticVar();// output 3
	IncrementStaticVar();// output 4
	IncrementStaticVar();// output 5
	SingleTon::Get();
	std::cin.get();

}