Pokemon type chart: is it mathematically worked out and are there exceptions?

[SendpkmNOOB]

As of alpha sapphire / omega ruby, there are more Pokemon and types. I'm currently writing a program for a pokedex where you type in a name and it gives you info on that Pokemon. What I wanna know is if you look at the type chart, do dual types just multiply the things together?
Example: a water/grass type
Normal effectiveness = 1x1 =1
Fire effectiveness = 1/2 x 2 = 1
Etc.
does it work like this or is there some other system, and if this is the case, are there exceptions to this rule in alpha sapphire / omega ruby. Need to know for my program, thanks.

 

[Pinball Wizard]

I believe that's the way it works, and if not technically, it would at least add up with all possible scenarios. You'd want to also account for Abilities, of course, depending on how in-depth you're getting.

 

[Alolan Coconut]

I think such a program is pretty useful for beginning players. After a while you'll memorize every type and their strengths, weaknesses and abilities. A program like that could be trustworthy, but in that case you have to be aware of abilities such as Wonder Guard, Levitate etc.

 

[Stratelier]

What I wanna know is if you look at the type chart, do dual types just multiply the things together?
Example: a water/grass type
Normal effectiveness = 1x1 =1
Fire effectiveness = 1/2 x 2 = 1

That is absolutely correct, if you have a dual-typed Pokemon whose types are weak and resistant to a type of attack, the attack does normal 1x effectiveness and will not be declared super/not very effective. Example: The whole Lotad family is Grass+Water type and does indeed take 1x damage from Fire (also Electric, Grass, and Ice) attacks.

The only exceptions to the type chart are with things like weather and abilities:

- Defending Pokemon has Filter or Solid Rock: Substitute 1.5x for 2x
- Defending Pokemon has Wonder Guard: Receives zero damage if effectiveness <= 1x
- Attacking Pokemon has Tinted Lens: Doubles damage if effectiveness < 1x
- Sunlight: Reduce all Water attacks to 0.5x, boost Fire attacks to 1.5x
- Rain: Reduce Fire attacks to 0.5x, boost Water to 1.5x
- (etc.)

However these are generally damage modifiers and not type modifiers, e.g. an attack will still be reported as normal / super / not very effective regardless of whether the ability boosted or weakened the actual damage.

 

[Pokepal148]

There is one other exception: the ice type move Freeze-Dry has the ability to hit water types for super effective damage.