Function NameGen(): attempt to compare nil with number

Question

The error I'm getting is

[string "function NameGen()..."]:14: attempt to compare nil with number
stack traceback:
    [string "function NameGen()..."]:14: in function 'NameGen'
    [string "function NameGen()..."]:23: in main chunk
    [C]: ?

My code:

function NameGen()
  preftest = math.random(100) ;
  syltest = math.random(100) ;
  sufftest = math.random(100) ;
  pref1 = "New ";
  _1syl1 = "Lon";
  _2syl1 = "Don";
  suff1 = " City";
  prefchoice = pref1;
  _1sylchoice = _1syl1;
  _2sylchoice = _2syl;
  suffchoice = suff1;

  if preftest < 50 and _2syltest < 50 and sufftest < 50 then 
    cityname = prefchoice .. _1sylchoice .. _2sylchoice .. suffchoice;
  elseif preftest < 50 and _2syltest < 50 then
    cityname = prefchoice .. _1sylchoice .. _2sylchoice;
  else
    cityname = _1sylchoice;
  end
end
NameGen();
print(cityname);

Answer 1

I don't see where _2syltest is being assigned -- only syltest . If _2syltest isn't coming from somewhere else, that could be the issue, since that's the condition in your if uses that value.

Answer 2

From the structure of your code it seems that you wanted to use syltest < 50 in both if and elseif conditions, instead you used _2sylchoice < 50 . Moreover probably you meant _2sylchoice = _2syl1 (a typo there?).

See if this is what you meant:

function NameGen()
  preftest = math.random(100) 
  syltest = math.random(100) 
  sufftest = math.random(100)
  pref1 = "New "
  _1syl1 = "Lon"
  _2syl1 = "Don";
  suff1 = " City"
  prefchoice = pref1
  _1sylchoice = _1syl1
  _2sylchoice = _2syl1
  suffchoice = suff1

  if preftest < 50 and syltest < 50 and sufftest < 50 then
    cityname = prefchoice .. _1sylchoice .. _2sylchoice .. suffchoice
  elseif preftest < 50 and syltest < 50 then
    cityname = prefchoice .. _1sylchoice .. _2sylchoice
  else
    cityname = _1sylchoice
  end
end

for i = 1, 100 do
    NameGen()
    print(cityname)
end

As an aside, you are using way too much global variables. All the variables you use should be local ones unless you have a strong reason to do otherwise (although I didn't change this aspect of your code in order not to confuse you in the case you weren't aware of what I'm talking about).