We have demonstrated the different type of arithmetic operators (+, -, *, / and ^), but there is one operator we have yet to mention. The modulo operator, for which we use the character %.

local a = 17
local b = 5
print(a % c) -- Output: 2

Modulo calculates the remainder. In the example above, the output is 2. That is because, if you keep extracting 5 from 17, 2 is what remains.

• 17 - 5 = 12
• 12 - 5 = 7
• 7 - 5 = 2 ✔️
• 2 - 5 = -3 ❌

The modulo operator is extremely useful. For example, we can use it to check if a number is odd or even.

local function odd_or_even(n)
    if n % 2 == 0 then
        print("Even!")
    else
        print("Odd!")
    end
end

odd_or_even(5) -- Output: Odd!
odd_or_even(200) -- Output: Even!
odd_or_even(486) -- Output: Even!
odd_or_even(7295621) -- Output: Odd!

Or we can check which day of the week a certain date is.

local days = {
    "Monday", "Tuesday", "Wednesday",
    "Thursday", "Friday", "Saturday",
    "Sunday"
}

local function check_day(date)
    print(days[(date - 1) % 7 + 1])
end

check_day(5) -- Output: Friday
check_day(14) -- Output: Sunday
check_day(32) -- Output: Thursday
check_day(38285) -- Output: Tuesday

The line days[(date - 1) % 7 + 1] includes the - 1 and + 1 because the first element in a Lua table is at index 1. Without, check_day(14) would turn into 14 % 7, which results into 0, and there is nothing to be found at days[0].

To prevent this, we use this trick:

1. Decrease date by 1 (14 - 1).
2. Now the modulo operator checks 13 % 7, which results into 6.
3. We increase the number by 1 (6 + 1).