[lua][error] Numbers and strings

I am trying to make a remote printing program, kinda like a wifi printer. I am having trouble with the string to number conversion/comparison. I know I have multiple errors; some in the client, some in the server, but the most prominent is on line 30 which produces:

print:30: attempt to compare string with number expected, got string

term.clear()
term.setCursorPos(1,1)
local printing = true
local page = true
repeat
  rednet.send(49,"newPage")
  local id,msg = rednet.receive(5)
  if msg == "true" then
	page = true
  elseif msg == "false" then
	page = false
  else
	print(msg)
	print(" ")
	page = false
  end
  if page == false then
	printing = false
  end
  local line = 1
  rednet.send(49,"getSize")
  local id,w = rednet.receive(5)
  local id,h = rednet.receive(5)
  repeat
	local l = read()
	if l == "exit" then
	  rednet.send(49,"finish")
	  printing = false
	  line = h
	elseif string.len(l) <= w then
	  rednet.send(49,l)
	  line = line + 1
	  rednet.send(49,"setLine," .. line)
	else
	  print("Line is too long. Max is: " .. w)
	end
  until line == h
  rednet.send(49,"endPage")
until printing == false
if page == false then
  print("Out Of Paper.")
end

local id,w = rednet.receive(5)
local id,h = rednet.receive(5)
--should be
local id,tonumber(w) = rednet.receive(5)
local id,tonumber(h) = rednet.receive(5)

The second variable returned by rednet.receive() is a string, so if you are sending numbers, you need to convert them to numbers before you can compare them. You can't compare numbers to strings.

I agree with cranium.
If you're sending numbers of rednet put them both as strings because it compares faster

Cranium, on 10 December 2012 - 07:15 AM said:

local id,w = rednet.receive(5)
local id,h = rednet.receive(5)
--should be
local id,tonumber(w) = rednet.receive(5)
local id,tonumber(h) = rednet.receive(5)

The second variable returned by rednet.receive() is a string, so if you are sending numbers, you need to convert them to numbers before you can compare them. You can't compare numbers to strings.

That gave me the error:

bios:338: [string "print"]:22: syntax error

so I tried:

local id,w = rednet.receive(5)
local id,h = rednet.receive(5)
w = tonumber(w)
h = tonumber(h)

and got:

print:32: attempt to compare nil with number

If w or h cannot be turned into a number, tonumber is returning nil instead, so it tries to compare nil to string.len(l). What do the messages look like that its receiving?

OK, so the server is what my problem is…
Here is the server code:

rednet.open("front")
local printer = peripheral.wrap("left")
local curID = ""
function parse(command,id)
  if command == "newPage" then
	local page = printer.newPage()
	rednet.send(id,page)
  elseif command == "getSize" then
	local w,h = printer.getPageSize()
	rednet.send(id,w)
	rednet.send(id,h)
  elseif command == "finish" then
	printer.endPage()
	curID = ""
  elseif command == "endPage" then
	printer.endPage()
  elseif string.find(command, "setLine,") ~= nil then
	local line = string.sub(command,string.find(command,",") + 1)
	printer.setCursorPos(1,line)
  else
	rednet.send(id,"Invalid Command")
  end
end
while true do
  local id,msg = rednet.receive()
  if curID ~= "" and id == curID then
	parse(msg,id)
  elseif curID == "" then
	curID = id
	parse(msg)
  elseif id ~= curID then
	rednet.send(id,"Printer In Use.")
  end
end

I managed to get it working myself.

Client:

shell.run("clear")
term.setTextColor(colors.red)
local printing = true
local page = true
repeat
  rednet.send(49,"newPage")
  local id,msg = rednet.receive(1)
  if msg == "true" then
    page = true
  elseif msg == "false" then
    page = false
  else
    print(msg)
    print(" ")
    printing = false
  end
  if page == false then
    printing = false
  end
  local line = 1
  rednet.send(49,"getSize")
  local id,w = rednet.receive(1)
  local id,h = rednet.receive(1)
  w = tonumber(w)
  h = tonumber(h)
  print(" ")
  repeat
    local l = read()
    if l == "exit" then
	  rednet.send(49,"finish")
	  printing = false
	  line = h
    elseif string.len(l) < w then
	  rednet.send(49,l)
	  line = line + 1
	  rednet.send(49,"setLine," .. line)
    else
	  print("Line is too long. Max is: " .. w)
    end
  until line == h
  if printing then
    rednet.send(49,"endPage")
  end
until printing == false
if page == false then
  print("Out of Paper.")
end

Server:

rednet.open("front")
local printer = peripheral.wrap("left")
local curID = ""
function parse(command,id)
  if command == "newPage" then
    local page = printer.newPage()
    rednet.send(id,tostring(page))
  elseif command == "getSize" then
    local w,h = printer.getPageSize()
    rednet.send(id,tostring(w))
    rednet.send(id,tostring(h))
  elseif command == "finish" then
    printer.endPage()
    curID = ""
  elseif command == "endPage" then
    printer.endPage()
  elseif string.find(command, "setLine,") ~= nil then
    local line = tonumber(string.sub(command,string.find(command,",") + 1))
    printer.setCursorPos(1,line)
  else
    printer.write(command)
  end
end
while true do
  local id,msg = rednet.receive()
  if curID ~= "" and id == curID then
    parse(msg,id)
  elseif curID == "" then
    curID = id
    parse(msg,id)
  elseif id ~= curID then
    rednet.send(id,"Printer In Use.")
  end
end