D&D Character

Instructions

For a game of Dungeons & Dragons, each player starts by generating a character they can play with. This character has, among other things, six abilities; strength, dexterity, constitution, intelligence, wisdom and charisma. These six abilities have scores that are determined randomly. You do this by rolling four 6-sided dice and recording the sum of the largest three dice. You do this six times, once for each ability.

Your character's initial hitpoints are 10 + your character's constitution modifier. You find your character's constitution modifier by subtracting 10 from your character's constitution, divide by 2 and round down.

Write a random character generator that follows the above rules.

For example, the six throws of four dice may look like:

• 5, 3, 1, 6: You discard the 1 and sum 5 + 3 + 6 = 14, which you assign to strength.
• 3, 2, 5, 3: You discard the 2 and sum 3 + 5 + 3 = 11, which you assign to dexterity.
• 1, 1, 1, 1: You discard the 1 and sum 1 + 1 + 1 = 3, which you assign to constitution.
• 2, 1, 6, 6: You discard the 1 and sum 2 + 6 + 6 = 14, which you assign to intelligence.
• 3, 5, 3, 4: You discard the 3 and sum 5 + 3 + 4 = 12, which you assign to wisdom.
• 6, 6, 6, 6: You discard the 6 and sum 6 + 6 + 6 = 18, which you assign to charisma.

Because constitution is 3, the constitution modifier is -4 and the hitpoints are 6.

Randomness in Zig

The Zig standard library avoids hidden global state, so rather than keeping a random number generator of your own, your functions receive a std.Random interface to draw values from. The tests pass in a generator seeded with std.testing.random_seed, and check that generators with the same seed produce the same characters.

Checking randomness

The distribution of your ability scores is checked by chi-squared tests at a significance level of p < 0.0001:

• the scores returned by ability are compared with the expected distribution;
• each of a character's six abilities is compared with the expected distribution;
• the pattern of odd and even scores across a character's six abilities is compared with what independent abilities would produce.

A correct implementation has less than a 0.01% chance of failing each test.

See the instructions above for a definition of what an ability score is.

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Source

Simon Shine, Erik Schierboom