CODEWITHSUNDEEP
lua
NeonStranger
NeonStranger

Reputation: 15

How do I get the first two digits from a number?

I need to make a code that tells you the century when you give the year. I have this:

local kata = {}

function kata.century(number)
  if number%100 == 0 then >I need to get the first two numbers
    return 
  else 
    return number/100 + 1
  end
end

return kata

I basically need a line that gives me the first two numbers of the year for years like "1700" and "2000" so I can divide them by 100 and add 1. (i'm a beginner btw)

Upvotes: 1

Views: 1786

Answers (2)

ad absurdum
ad absurdum

Reputation: 21318

According to the Gregorian calendar, 1 CE was the first year of the 1st Century CE. Since a century is a period of 100 years, this means that the first year of any century in the common era ends with a 1; thus 2000 was the last year of the 20th Century, and 2001 was the first year of the 21st Century.

Finding the century from the first two digits of the year alone will not work for this strictly correct method of identification. Taking the first two digits of 2000, and adding 1 would yield the 21st Century. But, instead of using math.floor to truncate the result of division by 10, one can use math.ceil to get the smallest integer greater than the result of the division.

function century (year)
  return math.ceil(year / 100)
end

This century function gives the correct century given a year in the common era:

> century(1)
1
> century(100)
1
> century(101)
2
> century(2000)
20
> century(2001)
21

There is a convention in popular usage that centuries should be numbered based on shared digits instead of the Gregorian calendar. In this usage all years beginning with 20 are in the 21st Century, making 2000 the first year of the 21st Century. Since there is no year 0 in the Gregorian calendar, this means that the 1st Century (from 1 CE to 99 CE under this convention) spans 99 years, but all other centuries in the common era span 100 years (e.g., 100 CE to 199 CE). Finding the century from the year using this convention can be done by dividing the year by 100 and taking the floor of the result.

If the goal is to match popular expectations and follow the general popular misunderstanding of numbering centuries, use the floor method. But, if the goal is to get correct and consistent numbering of centuries based on the Gregorian calendar, use the ceiling method.

Upvotes: 0

lhf
lhf

Reputation: 72312

In Lua 5.3+, use number//100.

For earlier versions, use math.floor(number/100).

Upvotes: 1

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