Check, If Read() Results Are Nil

Here`s my code;

term.clear()
os.loadAPI("Apis/DesignUtil")
DesignUtil.setDesign("whiteLightGray")
os.loadAPI("Apis/windowSystem")
local backGround,topBar=DesignUtil.getDesign()
local window=windowSystem.createWindow("System setup",2,2,48,16,false)
local slide=0
local U = nil
local P=nil;
local setupTexts=
{
s0="Please Enter your OSOne ID, or leave fields ";
s01="blank."

}

function registerClick(xPos,yPos)
if slide==0 then
	 if xPos >= createIDButton.x and xPos <= createIDButton.x + createIDButton.W - 1 and yPos >= createIDButton.y and yPos <=  createIDButton.y + createIDButton.H then
	  os.reboot()
	 end
end
end

function verifyData(Un,Pn)
if not Un and not Pn then
  slide=1
end
end

while true do
	  
term.setTextColor(colors.lightGray);
paintutils.drawImage(backGround,1,1)
if slide==1 then
end
if slide==0 then
term.setCursorPos(4,4)
  term.setTextColor(colors.gray);
print(setupTexts.s0)
term.setCursorPos(4,5)
print(setupTexts.s01)
  term.setTextColor(colors.lightGray);

end
windowSystem.drawWindow(window)
term.setBackgroundColor(colors.white)
if slide==0 then
  --button
   term.setBackgroundColor(colors.gray)
   term.setCursorPos(38,6)
  print("		   ")
  
  term.setCursorPos(20,6)
  term.setBackgroundColor(colors.white)
 
print("OSOne ID Username: ")
term.setCursorPos(38,6)
    term.setBackgroundColor(colors.gray)
term.setTextColor(colors.lightGray);
  U=read()
	 term.setBackgroundColor(colors.white)
term.setTextColor(colors.gray);
  term.setCursorPos(20,7)
print("OSOne ID Password: ")
    term.setBackgroundColor(colors.gray)
term.setCursorPos(38,7)
   print("		  ")
term.setCursorPos(38,7)
  term.setTextColor(colors.lightGray);
   P=read("*")
verifyData(U,P)
	 term.setBackgroundColor(colors.white)

end

sleep(0.15)
end

as you can see, if tha two fields have been Entered, it is supposed to run verifyData, it doesnt, verifyData does not set slide to 1, as that would clear the screen from the text but the screen stays the same. How can I make that work?

As i understood then here's my explanation:

This code is never setting slide to 1 unless Username AND Password hasn't been entered (is nil)

function verifyData(Un, Pn)
if not Un and not Pn then -- checks if Un and Pn is false or nil
slide = 1 -- then sets slide to 1..
end
end

Therefore slide will never be set to 1.
Deleting the "not" will make it set slide to 1 IF both Un and Pn is true.

function verifyData(Un, Pn)
if Un and Pn then
slide = 1
end
end

Else, as the title says then do:

U=read()
P=read("*")
if U ~= nil and P ~= nil then
 verifyData(U,P)
end

If this wasn't the way you want it, then tell me

I hope that'd help

read() never returns nil, it returns an empty string ( "" ) if nothing was entered.

Well then edit to this:

U=read()
P=read()
if U ~= "" and P ~= "" then
verifyData(U,P)
end

as easy as it is