Calculator

-- ShadOS Calculator by PaymentOption --
VERSION = "Alpha 1.0"
----------------------------------------

-- VARS --
sExpression = ""
nAnswer = nil
screenWidth, screenHeight = term.getSize()
selection = 1
----------

-- Helper Functions --
function cPrint(height, string)
    local xPos = screenWidth/2 - string.len(string)/2
    term.setCursorPos(xPos, height); term.write(string)
end

function rPrint(height, string)
    local xPos = screenWidth - string.len(string)
    term.setCursorPos(xPos, height); term.write(string)
end

function clear() term.clear(); term.setCursorPos(1,1) end

function split(str, pat)
   local t = {}  -- NOTE: use {n = 0} in Lua-5.0
   local fpat = "(.-)" .. pat
   local last_end = 1
   local s, e, cap = str:find(fpat, 1)
   while s do
      if s ~= 1 or cap ~= "" then
     table.insert(t,cap)
      end
      last_end = e+1
      s, e, cap = str:find(fpat, last_end)
   end
   if last_end <= #str then
      cap = str:sub(last_end)
      table.insert(t, cap)
   end
   return t
end
----------------------

-- Application related functions --
function printLogo()
    term.setCursorPos(2, 2)
    print("   -_-/  ,,           |\\     ,-||-,     -_-/  ")
    print("  (_ /   ||      _     \\\\   ('|||  )   (_ /   ")
    print(" (_ --_  ||/\\\\  < \\,  / \\\\ (( |||--)) (_ --_  ")
    print("   --_ ) || ||  /-|| || || (( |||--))   --_ ) ")
    print("  _/  )) || || (( || || ||  ( / |  )   _/  )) ")
    print(" (_-_-   \\\\ |/  \\/\\\\  \\\\/    -____-   (_-_-   ")
    print("           _/                                 ")

    print("           ,- _~.       ,,      ")
    print("          (' /|     _   ||      ")
    print("         ((  ||    < \\, ||  _-_ ")
    print("         ((  ||    /-|| || ||   ")
    print("          ( / |   (( || || ||   ")
    print("           -____-  \\/\\\\ \\\\ \\\\,/ ")
end

function printBorder() --Print Logo then border!
    local w,h = term.getSize()
    write(" ".. string.rep('*', w-2).."\n")
    for i=1, h-2 do write(" "..'*'..string.rep(" ", w-4)..'*'.."\n") end
    write(" ".. string.rep('*', w-2))

    cPrint(2, "ShadOS Calculator")
    rPrint(17, "Version: "..VERSION.."*")

    if bGetInput == true then cPrint(5, "Format: Num1 OPERATOR Num2") end
end

 function getInput()
    local nFirstNum = 0;
    local nSecondNum = 0;
    local cOperator = '';
    local tExpression = {}
    local sTempExpression = "" -- This will be used to grab the expression via read()

    bGetInput = true
    while true do
        clear()
        printBorder()
        term.setCursorPos(3,17); term.write("Write 'exit' to exit")
        if nAnswer ~= nil then term.setCursorPos(3, 3); term.write("ans: "..nAnswer..string.rep(" ", screenWidth-string.len("ans: "..nAnswer.."    "))) end

        term.write("*"..string.rep(" ", screenWidth-4).."*")
        term.setCursorPos(5, 7); term.write("Expression: ")
        sTempExpression = tostring(read())

        if sTempExpression == "exit" then bGetInput = false; break
        else
            tExpression = split(sTempExpression, " ")

            if tExpression[1] == "ans"then
                if nAnswer ~= nil then tExpression[1] = nAnswer
                else cPrint(8, "Error: No value held by prior answer"); sleep(1.3) end
            elseif tExpression[2] == "ans" then
                if nAnswer ~= nil then tExpression[1] = nAnswer
                else cPrint(8, "Error: No value held by prior answer"); sleep(1.3) end
            end
                nFirstNum = tExpression[1]
                cOperator = tExpression[2]
                nSecondNum = tExpression[3]

                -- Long ass operator checking.... --
                if cOperator == '+' then nAnswer = nFirstNum+nSecondNum; cPrint(8, "Answer: "..nAnswer); sleep(1.3)
                elseif cOpeartor == '-' then nAnswer = nFirstNum-nSecondNum; cPrint(8, "Answer: "..nAnswer); sleep(1.3)
                elseif cOperator == '*' then nAnswer = nFirstNum*nSecondNum; cPrint(8, "Answer: "..nAnswer); sleep(1.3)
                elseif cOperator == '/' then
                    if nSecondNum == 0 then cPrint(8, "Cannot divide by 0"); sleep(1.3)
                    else nAnswer = nFirstNum/nSecondNum; cPrint(8, "Answer: "..nAnswer); sleep(1.3) end
                elseif cOperator == '%' then nAnswer = nFirstNum%nSecondNum; cPrint(8, "Answer: "..nAnswer); sleep(1.3)
                else cPrint(8, "Invalid expression: Operator unknown."); sleep(1.3) end
        end
    end
end

function printMenu()
    if selection == 1 then cPrint(6, "[ Custom Expression ]")
    else                   cPrint(6, "  Custom Expression  ") end

    if selection == 2 then cPrint(7, "[ Exit ]")
    else                   cPrint(7, "  Exit  ") end
end
-----------------------------------

clear()
printLogo()
sleep(2)
while true do
    clear()
    printBorder()
    printMenu()

    event, key = os.pullEvent("key")

    if key == 200 and selection > 1 then selection = selection-1
    elseif key == 208 and selection < 2 then selection = selection+1

    elseif key == 28 and selection == 1 then getInput()
    elseif key == 28 and selection == 2 then clear(); break
    end
end