Singleton design pattern is a a creational pattern to 
dictate how and when objects get created and it's main 
purpose is to ensure that a class has only one instance

Example:
#define NULL 0

class Singleton
{
private:
	Singleton(Singleton&){}
	Singleton& operator =(Singleton&);
	int nValue;
	static Singleton* pSingleton;
	Singleton():nValue(10)
	{
	}
public:
	static Singleton*Instance()
	{

		if(NULL == pSingleton)
		{
			pSingleton = new Singleton();
		}
		return pSingleton;
	}
	void setValue(int val)
	{
		nValue = val;
	}
	int getValue()
	{
		return nValue;
	}
};
Singleton* Singleton::pSingleton = NULL;

int main(int argc, char* argv[])
{
	Singleton *abc = NULL;
	cout<<Singleton::Instance()->getValue()<<endl;
	Singleton::Instance()->setValue(20);

	Singleton *xyz = NULL;
	cout<<xyz->Instance()->getValue()<<endl;
	Singleton *sss = Singleton::Instance();
	return 0;
}