A simple dice roller for iPhones

The DieStructure uses an enumeration of the common table-top roleplaying game die types, called DieType, to determine the behavior of instances of the DieStructure.

• type: DieType -- Default initializer is d4. This denotes what type of die the instance is.
• totalDice: Int -- Default initializer is 1. Represented the number of dice to be rolled. For example, if two six sided die need to be rolled, then this value should be two.
• modifier: int -- Default initializer is 0. Represents the modifier that is to be added to the result of all the dice rolls of that type. totalDice and modifier, combined with the type property represent the short hand expressions used in table top RPGs to represent how many dice to roll, and the modifier added to that result, such as 2d6+3 represents two six sided die being rolled, and the integer value 3 being added to that. Using the properties of DieStructure: DieType is d6, totalDice is 2, and modifier is 3.

• mutating func addDie() -- Increments the totalDie property by 1. If totalDie would be greater than 99, it is set to 1, as 99 is the maximum number of die, and representing a negative or zero amount of die would be meaningless. This function is called when the user taps the plus button to the left of the roll button.
• mutating func removeDie() -- Decrements totalDie by 1. If the value is already at 1, it will remain at one, as representing a negative or zero amount of die would be meaningless. This function is called when the user taps the plus button to the left of the roll button.
• mutating func addModifier() -- Increments the modifier property by 1. If the modifier is greater than 99, it changes it to -99, as these are the maximum and minimum values for the modifier. This function is called when the user taps on the plus buttons to the right of the roll button.
• mutating func removeModifier() -- Decrements the modifier property by 1. This function is called when the user taps on the minus buttons to the right of the roll button.
• mutating func resetDie() -- Sets modifier and totalDie to 0 and 1 respectively. This function is called when the user taps the clear button.
• rollDie() -> Int -- This function produces a random number based on the type of die. It first uses a switch statment to determine which type of die is being rolled. Based on which type it is, a value is assigned to upperBound: UInt32. A variable is created to hold the value of the roll, rollValue: UInt32. An index variable i is created to be used as the exit condition for a while loop. In the while loop, arc4random_uniform(__upper_bound: UInt32) is used passing upperBound as its argument to generate a random number between 0 and the value of upperBound. The loop runs a number of times equal to the number of dice, represented by i, which id decermented during each loop. Finally, the value returned by rollDie() is the rollValue as an Int + 1 so it is within the correct range of values, plus the modifier to that roll. The modifier is applied after all the die are rolled, as is custom in most TTRPGs.