Pi

local circle = [[

            0000000
       00000000000000000
     000000000000000000000
   0000000000000000000000000
  000000000000000000000000000
  000000000000000000000000000
 00000000000000000000000000000
 00000000000000000000000000000
 00000000000000000000000000000
  000000000000000000000000000
  000000000000000000000000000
   0000000000000000000000000
     000000000000000000000
       00000000000000000
            0000000

]]

local diameter, circumfrence = 0, 0
local circletbl = {}

local x, y = 1, 1
for char in string.gmatch(circle, ".") do
    if not circletbl[x] then circletbl[x] = {} end

    if char == "\n" then
        x = 1
        y = y + 2 -- Because each '0' is 2 units tall
    else
        circletbl[x][y] = (char == "0")
        circletbl[x][y+1] = (char == "0") -- Because each '0' is 2 units tall
        x = x + 1
    end
end

local x = #circletbl[1] / 2
for y = 1, #circletbl do
    if circletbl[x][y] then
        diameter = diameter + 1
    end
end

print("Diameter of the circle is "..diameter)

for x, tbl in pairs(circletbl) do
    for y, val in pairs(tbl) do
        if val then
            if circletbl[x][y+1] == false or circletbl[x][y-1] == false or circletbl[x+1][y] == false or circletbl[x-1][y] == false then
                circumfrence = circumfrence + 1
            end
        end
    end
end

print("Circumfrence of the circle is "..circumfrence)

print("Pi is about equal to ".. circumfrence / diameter)