Some is scripted. They do a variety of other things too. For example, path finding gets its own algorithm. And they have algorithms for getting multiple guys to

Some is scripted. They do a variety of other things too. For example, path finding gets its own algorithm. And they have algorithms for getting multiple guys to move around in formation. Sometimes there is some type of system with goals (get 1000 wood, get an 80 food army, kill X base, etc) and then it picks things to achieve those goals (build more wood harvesters, build more units, attack). sometimes they use "learning" algorithms where they tweak parameters by running the AI repeatedly and seeing which does better, and they can use games with a human player to do that too (if it wins too badly, have it aim less precisely). And lots of other one-off things.