How do I add a critical chance mechanic to my game?

I'm making a turn based rpg game and was wondering how to add a critical chance mechanic to my game to increase the damage if its a critical hit.

When you do damage, pick a number from a range and based on the result decide if it's a critical hit, for example floor(random(100)) will pick an integer from 0-100 (not including 100). You could then say if the number picked is less than 25 then its a critical hit, for a 25% chance of a crit hit.

I'm sorry I'm a noob how would you code that in drag and drop?

Hmm there's a lot more complexity coming your way if you're attempting a turn based RPG, what is the drag and drop element for?

Your characters attack when you drag the object?

No that is the code method.

Someone redid my game and this is the current attacking function.

Instead of subtracting hp from the enemy, pull a floor (random (100)).

Then with two sub-events, subtract the damage.

If random is higher than 50 it can do normal damage, and if it is lower than 49 it can do critical damage (it's just an example).

I do not know if I explain myself well, my English is very bad.

Thank you now it's working.

Heres how it looks.