Fixed

term.setTextColor(colors.white)
local button = {}
term.setBackgroundColor(colors.black)

function CurPos()
 term.setCursorPos(4,4)
end

function drawCalc()
 term.clear()
 term.setCursorPos(2,2)
 term.setTextColor(colors.white)
 term.setBackgroundColor(colors.black)
 function printVerticalLine(lineX, startingY, endingY, lineColor)
  local curX, curY = term.getCursorPos()
  term.setBackgroundColor(lineColor)
  for lineY = startingY, endingY do
   term.setCursorPos(lineX, lineY)
   term.write(" ")
  end
  term.setCursorPos(curX, curY)
 end

function printHorizontalLine(yLine, startingX, endingX, lineColor)
  local curX, curY = term.getCursorPos()
  term.setBackgroundColor(lineColor)
  for xLine = startingX, endingX do
   term.setCursorPos(xLine, yLine)
   term.write(" ")
  end
  term.setCursorPos(curX, curY)
 end

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

function setTable(name, func, xmin, xmax, ymin, ymax)
 button[name] = {}
 button[name]["func"] = func
 button[name]["active"] = false
 button[name]["xmin"] = xmin
 button[name]["ymin"] = ymin
 button[name]["xmax"] = xmax
 button[name]["ymax"] = ymax
end

function fillTable()
 setTable("1",One,3,7,15,17)
 setTable("2",Two,9,13,15,17)
 setTable("3",Three,15,19,15,17)
 setTable("4",Four,3,7,11,13)
 setTable("5",Five,9,13,11,13)
 setTable("6",Six,15,19,11,13)
 setTable("7",Seven, 3,7,7,9)
 setTable("8",Eight, 9,13,7,9)
 setTable("9",Nine, 15,19,7,9)
end

function fill(text, color, bData)
   term.setBackgroundColor(color)
   local yspot = math.floor((bData["ymin"] + bData["ymax"]) /2)
   local xspot = math.floor((bData["xmax"] - bData["xmin"] - string.len(text)) /2) +1
   for j = bData["ymin"], bData["ymax"] do
      term.setCursorPos(bData["xmin"], j)
      if j == yspot then
         for k = 0, bData["xmax"] - bData["xmin"] - string.len(text) +1 do
            if k == xspot then
               term.write(text)
            else
               term.write(" ")
            end
         end
      else
         for i = bData["xmin"], bData["xmax"] do
            term.write(" ")
         end
      end
   end
   term.setBackgroundColor(colors.black)
end

function screen()
   local currColor
   for name,data in pairs(button) do
      local on = data["active"]
      if on == true then
       currColor = colors.gray
      else
       currColor = colors.black
      end
      fill(name, currColor, data)
   end
end

function checkxy(x, y)
   for name, data in pairs(button) do
      if y>=data["ymin"] and  y <= data["ymax"] and x>=data["xmin"] and x<= data["xmax"] then
            term.setCursorPos(1, 1)
            write(name)
            data["active"] = not data["active"]
            sleep(0.1)
            data["active"] = not data["active"]
            return true, name
         end
   end
   return false, nil
end
calc = ""
drawCalc()
fillTable()
screen()

while true do
   local e,button,x,y = os.pullEvent("mouse_click")
   bValid, numb = checkxy(x,y)
    if bValid then
        calc = calc .. numb
        term.setCursorPos(4, 4)
        if #calc < 14 then
            write(calc)
        else
            write(calc:sub(#calc-14))
        end
    end
end