Calcfix

buttonsMain = {}
buttonsExtra = {}
buttonsColors = {}

input = {nil, nil, nil}
calc = ""
screenX, screenY = term.getSize()

local color = colors.white

term.setBackgroundColor(colors.black)
term.setTextColor(colors.white)
term.clear()

function colorSet()
  if name == "White" then
   term.setBackgroundColor(colors.white)
  elseif name == "Orange" then
   term.setBackgroundColor(colors.orange)
  elseif name == "Magenta" then
   term.setBackgroundColor(colors.magenta)
  elseif name == "Light Blue" then
   term.setBackgroundColor(colors.lightBlue)
  elseif name == "Yellow" then
   term.setBackgroundColor(colors.yellow)
  elseif name == "Lime" then
   term.setBackgroundColor(colors.lime)
  elseif name == "Pink" then
   term.setBackgroundColor(colors.pink)
  elseif name == "Gray" then
   term.setBackgroundColor(colors.gray)
  elseif name == "Light Gray" then
   term.setBackgroundColor(colors.lightGray)
  elseif name == "Cyan" then
   term.setBackgroundColor(colors.cyan)
  elseif name == "Purple" then
   term.setBackgroundColor(colors.purple)
  elseif name == "Blue" then
   term.setBackgroundColor(colors.blue)
  elseif name == "Brown" then
   term.setBackgroundColor(colors.brown)
  elseif name == "Green" then
   term.setBackgroundColor(colors.green)
  elseif name == "Red" then
   term.setBackgroundColor(colors.red)
  elseif name == "Black" then
   term.setBackgroundColor(colors.black)
  end
end

function printVerticalLine(lineX, startingY, endingY)
    local curX, curY = term.getCursorPos()
    term.setBackgroundColor(colors.white)
    for lineY = startingY, endingY do
        term.setCursorPos(lineX, lineY)
        term.write(" ")
    end
    term.setCursorPos(curX, curY)
    term.setBackgroundColour(colours.black)
end

function printHorizontalLine(yLine, startingX, endingX)
    local curX, curY = term.getCursorPos()
    term.setBackgroundColor(colors.white)
    for xLine = startingX, endingX do
        term.setCursorPos(xLine, yLine)
        term.write(" ")
    end
    term.setCursorPos(curX, curY)
    term.setBackgroundColour(colours.black)
end

function drawTable()
    printVerticalLine(2,2,18)
    --Left Border
    printVerticalLine(20,2,18)
    --Right Border
    printVerticalLine(8,6,18)
    --Left Seperator
    printVerticalLine(14,6,18)
    --Right Seperator
    printHorizontalLine(2,2,20)
    --Top
    printHorizontalLine(6,2, 20)
    --Upper Before Keys
    printHorizontalLine(18,2,20)
    --Bottom
    printHorizontalLine(10,2,20)
    --Upper Seperator
    printHorizontalLine(14,2,20)
    --Lower Seperator
    term.setBackgroundColor(colors.black)
end

function drawFunctionsTable()
    printHorizontalLine(6,32,50)
    --Top
    printHorizontalLine(10,32,50)
    printHorizontalLine(14,32,50)
    printHorizontalLine(18,32,50)
    --Bottom
    printVerticalLine(32,6,18)
    --Left Border
    printVerticalLine(38,6,14)
    printVerticalLine(44,6,18)
    printVerticalLine(50,6,18)
    --Right Border
    term.setBackgroundColor(colors.black)
end

function drawColorsTable()
 printVerticalLine(2,2,18)
 --Left
 printVerticalLine(14,2,18)
 printVerticalLine(26,2,18)
 printVerticalLine(40,2,18)
 printVerticalLine(50,2,18)
end

function drawExtraButtonsTable()
    --Help, Color settings, 2nd button for filling table with ExtraFunctions
    printVerticalLine(23,6,18)
    --Left Border
    printVerticalLine(29,6,18)
    --Right Border
    printHorizontalLine(6,23,29)
    --Top
    printHorizontalLine(10,23,29)
    printHorizontalLine(14,23,29)
    printHorizontalLine(18,23,29)
    --Bottom
    term.setBackgroundColour(colours.black)
end

function setTable(_table, name, xMin, xMax, yMin, yMax)
    table.insert(_table, {
        numb = name,
        xmin = xMin,
        xmax = xMax,
        ymin = yMin,
        ymax = yMax
    })
end

function fillTable()
    setTable(buttonsMain, "1", 3, 7, 15, 17)
    setTable(buttonsMain, "2", 9, 13, 15, 17)
    setTable(buttonsMain, "3", 15, 19, 15, 17)
    setTable(buttonsMain, "4", 3, 7, 11, 13)
    setTable(buttonsMain, "5", 9, 13, 11, 13)
    setTable(buttonsMain, "6", 15, 19, 11, 13)
    setTable(buttonsMain, "7", 3, 7, 7, 9)
    setTable(buttonsMain, "8", 9, 13, 7, 9)
    setTable(buttonsMain, "9", 15, 19, 7, 9)
    setTable(buttonsExtra, "1", 3, 7, 15, 17)
    setTable(buttonsExtra, "2", 9, 13, 15, 17)
    setTable(buttonsExtra, "3", 15, 19, 15, 17)
    setTable(buttonsExtra, "4", 3, 7, 11, 13)
    setTable(buttonsExtra, "5", 9, 13, 11, 13)
    setTable(buttonsExtra, "6", 15, 19, 11, 13)
    setTable(buttonsExtra, "7", 3, 7, 7, 9)
    setTable(buttonsExtra, "8", 9, 13, 7, 9)
    setTable(buttonsExtra, "9", 15, 19, 7, 9)
end

function fillFunctionsTable()
    setTable(buttonsMain, "C", 33,37,7,9)
    setTable(buttonsMain, ".", 39,43,7,9)
    setTable(buttonsMain, "/", 45,49,7,9)
    setTable(buttonsMain, "+", 33,37,11,13)
    setTable(buttonsMain, "-", 39,43,11,13)
    setTable(buttonsMain, "*", 45,49,11,13)
    setTable(buttonsMain, "0", 33,43,15,17)
    setTable(buttonsMain, "=", 45,49,15,17)
end

function fillExtraFunctions()
    setTable(buttonsExtra, "^", 33,37,7,9)
    setTable(buttonsExtra, "rt", 39,43,7,9)
    setTable(buttonsExtra, "/", 45,49,7,9)
    setTable(buttonsExtra, "+", 33,37,11,13)
    setTable(buttonsExtra, "-", 39,43,11,13)
    setTable(buttonsExtra, "*", 45,49,11,13)
    setTable(buttonsExtra, "0", 33,43,15,17)
    setTable(buttonsExtra, "=", 45,49,15,17)
end

function fillExtraButtonsTable()
    setTable(buttonsExtra, "F",24,28,7,9)
    setTable(buttonsExtra, "H",24,28,11,13)
    setTable(buttonsExtra, "c",24,28,15,17)
    setTable(buttonsMain, "F",24,28,7,9)
    setTable(buttonsMain, "H",24,28,11,13)
    setTable(buttonsMain, "c",24,28,15,17)
end

function fillColorOptions()
 setTable(buttonsColors,"White",3,13,3,5)
 setTable(buttonsColors,"Orange",3,13,7,9)
 setTable(buttonsColors,"Magenta",3,13,11,13)
 setTable(buttonsColors,"Light Blue",3,13,15,17)
 setTable(buttonsColors,"Yellow",15,25,3,5)
 setTable(buttonsColors,"Lime",15,25,7,9)
 setTable(buttonsColors,"Pink",15,25,11,13)
 setTable(buttonsColors,"Gray",15,25,15,17)
 setTable(buttonsColors,"Light Gray",27,37,3,5)
 setTable(buttonsColors,"Cyan",27,37,7,9)
 setTable(buttonsColors,"Purple",27,37,11,13)
 setTable(buttonsColors,"Blue",27,37,15,17)
 setTable(buttonsColors,"Brown",39,49,3,5)
 setTable(buttonsColors,"Green",39,49,7,9)
 setTable(buttonsColors,"Red",39,49,11,13)
 setTable(buttonsColors,"Black",39,49,15,17)
end

function checkClick(tab, mx, my)
    for i, v in pairs(tab) do
        if mx >= v.xmin and mx <= v.xmax and my >= v.ymin and my <= v.ymax then
            return true, v.numb
        end
    end
    return false, nil
end

function screen(tab)
    term.setBackgroundColour(colours.black)
    term.setTextColour(colours.white)
    for name, data in pairs(tab) do
        local yspot = (data["ymin"] + data["ymax"]) / 2
        local xspot = (data["xmin"] + data["xmax"]) / 2
        term.setCursorPos(xspot, yspot)
        colorSet()
        --should be sets background of the color to its name
        write(data.numb)
    end
end

function redraw()
    term.setCursorPos(4, 4)
    write(string.rep(" ", 15))
    term.setCursorPos(4, 4)
end

function displayHelp()
    term.setBackgroundColour(colours.white)
    term.setCursorPos(1, 1)
    term.clear()

    term.setBackgroundColour(colours.grey)
    write(string.rep(" ", screenX))

    term.setBackgroundColour(colours.red)
    term.setCursorPos(screenX, 1)
    write("X")

    term.setBackgroundColour(colours.white)
    term.setTextColour(colours.black)
    term.setCursorPos(1, 2)
    print("There will be help here once I decide to not be lazy and fill it out, for now check the forums!")

    repeat local _, but, x, y = os.pullEvent("mouse_click") until but == 1 and x == screenX and y == 1

    term.setBackgroundColour(colours.black)
    term.clear()

    drawTable()
    screen(buttonsMain)
    drawFunctionsTable()
    drawExtraButtonsTable()
end

function setInput1()
    input[1] = tonumber(calc) or input[1]
    input[2] = numb
    redraw()
    calc = ""
    numb = ""
end

function enterPress()
    input[3] = tonumber(calc)
    redraw()
    calc = ""
    if input[2] == "+" then
        Output = input[1] + input[3]
    elseif input[2] == "-" then
        Output = input[1] - input[3]
    elseif input[2] == "*" then
        Output = input[1] * input[3]
    elseif input[2] == "/" then
        Output = input[1] / input[3]
    elseif input[2] == "^" then
        Output = input[1] ^ input[3]
    elseif input[2] == "rt" then
        Output = math.sqrt(input[1])
    end
    write(Output)
    input[1] = Output
end
--[[ Running Code ]]--

-- Run the functions to fill the table with math functions
fillExtraFunctions()
fillTable()
fillFunctionsTable()
fillExtraButtonsTable()

-- Run the functions to draw the tables
drawTable()
drawFunctionsTable()
drawExtraButtonsTable()

screen(buttonsMain)
state = "main"

while true do
    local e, but, x, y = os.pullEvent("mouse_click")
    if but == 1 then
        bValid, numb = checkClick(state == "main" and buttonsMain or state == "extra" and buttonsExtra, x, y)
        if bValid then
            if numb == "+" then
                setInput1()
            elseif numb == "-" then
                setInput1()
            elseif numb == "*" then
                setInput1()
            elseif numb == "/" then
                setInput1()
            elseif numb == "^" then
                setInput1()
            elseif numb == "rt" then
                setInput1()
            elseif numb == "H" then
                displayHelp()
            elseif numb == "F" then
                drawTable()
                drawFunctionsTable()
                drawExtraButtonsTable()
                if state == "main" then
                    state = "extra"
                    screen(buttonsExtra)
                elseif state == "extra" then
                    state = "main"
                    screen(buttonsMain)
                end
            elseif numb == "=" then
                enterPress()
            elseif numb == "c" then
                 term.clear()
                 drawColorsTable()
                 screen(buttonsColors)
                 if numb == "White" then
                  color = colors.white
                 elseif numb == "Orange" then
                  color = colors.orange
                 elseif numb == "Magenta" then
                  color = colors.magenta
                 elseif numb == "Light Blue" then
                  color = colors.lightBlue
                 elseif numb == "Yellow" then
                  color = colors.yellow
                 elseif numb == "Lime" then
                  color = colors.lime
                 elseif numb == "Pink" then
                  color = colors.pink
                 elseif numb == "Gray" then
                  color = colors.gray
                 elseif numb == "Light Gray" then
                  color = colors.lightGray
                 elseif numb == "Cyan" then
                  color = colors.cyan
                 elseif numb == "Purple" then
                  color = colors.purple
                 elseif numb == "Blue" then
                  color = colors.blue
                 elseif numb == "Brown" then
                  color = colors.brown
                 elseif numb == "Green" then
                  color = colors.green
                 elseif numb == "Red" then
                  color = colors.red
                 elseif numb == "Black" then
                  color = colors.black
                 end

                 term.clear()
                 fillExtraFunctions()
                 fillTable()
                 fillFunctionsTable()
                 fillExtraButtonsTable()

                 drawTable()
                 drawFunctionsTable()
                 drawExtraButtonsTable()

                 screen(buttonsMain)
                 state = "main"
            elseif numb == "C" then
                for i = 1,3 do
                    input[i] = nil
                end
                calc = ""
                redraw()
            elseif numb == "." then
                calc = calc .. numb
                term.setCursorPos(4,4)
                if #calc < 14 then
                    write(calc)
                else
                    write(calc:sub(#calc-14))
                end
            elseif tonumber(numb) then -- if it is a number
                calc = calc .. numb
                term.setCursorPos(4, 4)
                if #calc < 14 then
                    write(calc)
                else
                    write(calc:sub(#calc-14))
                end
            end
        end
    end
end