health;
Real(实数)
This built in instance variable is used to hold a numeric value for the object health (note that this is not necessarily always the case - just because it's called "health" doesn't mean it has to be used for the health... it can hold any real or integer value you wish for your game).
if place_meeting(x, y, obj_Enemy)
{
health -= 10;
if health <= 0 instance_destroy();
}
The above code checks the current instance to see if there is a collision with the instance of the object indexed in "obj_Enemy", and if there is, it removes 10 points from the health variable and then checks this value to see if it is less than or equal to 0. 如果是实例会摧毁自己。