calculator

sin = 0
function menu(text, id)
  if sin == id then
        write("[ "..text.."  ]")
  else
        write("  "..text.."   ")
  end
  print""
end
term.clear()
term.setCursorPos(1,1)
print"Enter First Number"
write""
input = tonumber(read())
term.clear()
term.setCursorPos(1,1)
print"Select A Symbol"
while true do
term.setCursorPos(1,4)
menu("+", 0)
menu("-", 1)
menu("/", 2)
menu("*", 3)

local event, key = os.pullEvent("key")
if key == 208 then
  if sin > 2 then
        sin = sin - 2
  else
        sin = sin + 1
  end
elseif key == 200 then
  if sin < 1 then
        sin = sin + 2
  else
        sin = sin - 1
  end
elseif key == 28 then
  if sin == 0 then
        term.clear()
        term.setCursorPos(1,1)
        print"Enter Second Number"
        write""
        input2 = tonumber(read())
        output = input2 + input
        term.clear()
        term.setCursorPos(1,1)
        print(output.."         Press Enter To Continue")
        sleep(5)
        if key == 28 then
          term.clear()
          term.setCursorPos(1,1)
          return
        end
      end
  if sin == 1 then
        term.clear()
        term.setCursorPos(1,1)
        print"Enter Second Number"
        write""
        input2 = tonumber(read())
        output = input - input2
        term.clear()
        term.setCursorPos(1,1)
        print(output.."         Press Enter To Continue")
        sleep(5)
        if key == 28 then
          term.clear()
          term.setCursorPos(1,1)
          return
        end
        end
  if sin == 2 then
        term.clear()
        term.setCursorPos(1,1)
        print"Enter Second Number"
        write""
        input2 = tonumber(read())
        output = input / input2
        term.clear()
        term.setCursorPos(1,1)
        print(output.."         Press Enter To Continue")
        sleep(5)
        if key == 28 then
          term.clear()
          term.setCursorPos(1,1)
          return
        end
        end
  if sin == 3 then
        term.clear()
        term.setCursorPos(1,1)
        print"Enter Second Number"
        write""
        input2 = tonumber(read())
        output = input2 * input
        term.clear()
        term.setCursorPos(1,1)
        print(output.."         Press Enter To Continue")
        sleep(5)
        if key == 28 then
          term.clear()
          term.setCursorPos(1,1)
          return
        end
    end
  end
end