Finding distance between two objects?

Hey there, I want to find the distance between two objects, and use that distance so that if its less than a certain amount, a certain something will happen.

Also, How would I create this, at the moment I have a zombie, and if it has LOS to the Player, it will set a waypoint at the players position. However this causes the zombie to move to the players last position, and makes the game easy to play. I want to have it so that the zombie will always move towards the players current position, and not going to its last waypoint before doing so.

Distance(Object1.x,Object1.y,Object2.x,Object2.y) Will give you the distance between 2 objects.

Could you not simply update the Zombie's waypoint every second or so as your player is moving?

Even when I do that, the zombie still has to go to the past waypoint before it chooses to create another at the player. Previous waypoints are not overwritten by new ones.