map making help

[raaaaaa]

I'm making a ums map that's supposed to blend offence with defence, but some of my triggers aren't working the way I want them to. The goal is to have the 'attackers' send up how ever many units they want to attack and the computer will automatically respond according to how many were sent. for instance: if 1 marine was sent, then the first retaliation is sent. if 20 marines are sent, then the second is sent. etc... right now I'm using the player brings at least # to 'location' trigger to do this, but it's not working the way I described. What I think I need is a sort of counter of how many units have been sent to that location previously. and based on what the counter's value is, send the retaliation units. Is there a way to do it this way or would I have to use a switch, which I've never used?

[stickynote]

You can use death counters, and if you don't know what they are, I'll explain.
This is the counter:
Players: Whoever you want, but I will use player 1 in this example
Conditions:
-Player 1 has suffered exactly 0 deaths of "Cave-In" (You can use any unit that you don't use in your map, but unused units are the best)
-Player 1 Brings 20 marines to location "raaaaaa was here"
Actions:
-Modify Death Counts for Player 1: Set to 20 for "Cave-In"
-Preserve Trigger
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Cave-Ins can be a representation for marines.
Then, for the computer to send 20 marines later, or whatever retaliation you want after your fight with them is over, you can have:
Players: The Computer, but I will call it Player 2
Condtitions:
-Player 1 has suffered exactly 20 deaths of "Cave-In"
You can have any other condition to have it at a more specific time, like Player 1 brings exactly 0 any unit to location "this is the comp's base"
Actions:
-Modify death counts for Player 1: Set to 0 for "Cave-In" (If you want to reset it."
-Create 20 marines for player 2 at location "Comp Spawn"
-Issue order to all units in location "comp spawn" to attack to location "player 1's base"
-Preserve trigger
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You can fiddle around with this and change the numbers and units.

[Specter]

Hi can someone tell me how to make it so that u can take over bases and stuff like Risk in Starcraft?