Problem with GetAsyncKeyState Function

//Function()

int Login_student::Switch_NP()                 //function in some student class
{
	int Button_Pressed=0;
	
	if(GetAsyncKeyState(VK_DOWN)!=0)
		Button_Pressed=1;
	else if(GetAsyncKeyState(VK_UP)!=0)
		Button_Pressed=10;
	else if(GetAsyncKeyState(VK_BACK)!=0)
		Button_Pressed=11;
	return Button_Pressed;
}
//in main()
while(1)
    {
        int num=Student.Switch_NP();     //Function for getting key(given above)
        switch(num)
            {
            case 1:                         //Down-key pressed Case
            {
                //it should run one time only
                break;
            }
            case 10:                            //Up-key Pressed
            {
                //it should run one time only
                break;
            }
            case 11:                           //Back_Space Pressed
            {
                //it should run one time only
                break;
            }
            default:
            {
                if(GetAsyncKeyState(VK_RETURN)!=0)       //Return key pressed
                {
                    //it should run one time only
                }
                break;
            }
        }
    }