why when i write 2 brackets after name object ,object not created ?!!

I doubt that only one of the objects is being created. Let's modify your code in the following way:

static int objId = 0;

class MyClass
{
public:
	MyClass() { cout << "Create object "<< objId  << endl; }	
};

void main()
{ 
        objId = 2;
	MyClass obj2(); //why when i write 2 brackets after name, object not created

        objId = 1;
	MyClass obj1;   //this statment create object
}

Now you can distinguish whether the first or the second call or both are being executed.

[AMENDED]
Apparently the C++ compiler interprets the first one (obj2) as a function prototype declaraction. It thinks you are declaring a function with name obj2 that takes no parameters and returns a value of type MyClass.

When I compile it with VC++ the compiler generates the warning:

prototyped function not called (was a variable definition intended?)

which indicates what's going on. If you would create an object via new, this syntax would be allowed, i.e:

MyClass* pObj2 = new MyClass();

Hope that helped clarify it.