# check: Work with skill checks' probabilities and DCs In droll: Analyze Roll Distributions

## Description

These are simple functions that manipulate probabilities and DCs for skill checks. `check_prob()` calculates the success/failure probability of a check with the given DC. `check_dc()` calculates the required difficulty class so that a skill check has the given success/failure probability. See below for more details.

## Usage

 ```1 2 3``` ```check_dc(roll, p, success = TRUE) check_prob(roll, dc, success = TRUE) ```

## Arguments

 `roll` A roll expression (e.g., `2 * d6 + 5`) or a data frame returned by `r()`. `p` The probability of success/failure of the check (or attack). `success` Whether to aim for success (the default) or for failure on the check (or attack). `dc` The difficulty class to beat for a skill check (or the armor class to beat for an attack).

## Details

These functions hide the complexities of the roll family so users unfamiliar with R's d/p/q/r notation can get quickly up and running with the package. Since attacks and checks work in the same way (i.e., success means rolling a value higher than or equal to a certain threshold), there are no `attack_*()` functions.

For more details on roll expressions, see `r()` and the Dice S4 class.

## Value

A numeric scalar.

roll, `r()`, Dice.
 ```1 2 3 4 5``` ```# Probability of d20 + 8 passing a DC 15 skill check check_prob(d20 + 8, 15) # Probability of d20 + 8 missing an AC 15 attack check_prob(d20 + 8, 15, success = FALSE) ```