Trying to receive a value from a user and increment it - lua

i'm new in progamming and starting with few basics tips. So my problem is: i'm trying to run a code that ask user a name and print it on screen, its run ok. So i'm trying to do something special now adding to code a part that ask the user how many times the name will be printed on screen, but when i do that it start a infinite loop and won't stop until i close the progam.
Here its the code
function metodoDois()
print("Write a name: ")
name = io.read();
print("Write how many times that it will be printed on screen: ")
quantidade = io.read()
k = 0;
while name do
k = k+1;
io.write("\n", name, " ", k)
if k == quantidade then
name = not name;
end
end
end
metodoDois()

Usually, to repeat a computation a known number of times, it is used a for loop. So, if you do not have specific reasons to use a while loop, you could go with:
function metodoDois()
print("Write a name:")
local name = io.read()
print("Write how many times that it will be printed on screen:")
local quantidade = io.read()
for k = 1, quantidade do
io.write("\n", name, " ", k)
end
end
metodoDois()
This way, you avoid explicitly creating the control variable k and to perform a test at each iteration in order to asses when to end it. In fact, the control variable k in the for-loopis automatically updated at each iteration, letting the loop end when such variable gets its final value.
Moreover, k is local to the for-loop (i.e., it doesn't exist before or after it), making the code more readable and less error prone (see: Local Variables and Blocks in the Lua Reference.)

The problem is your "quantidade" variable is being read as a string, while your "k" variable is a number. Numbers and strings are not alike, so, for example, 1 isn't the same as "1".
To fix this, simply convert the reading stored in the "quantidade" variable to a number first using the tonumber() function, by changing quantidade = io.read() to quantidade = tonumber(io.read()) like so:
function metodoDois()
print("Write a name: ")
name = io.read();
print("Write how many times that it will be printed on screen: ")
quantidade = tonumber(io.read())
k = 0;
while name do
k = k+1;
io.write("\n", name, " ", k)
if k == quantidade then
name = not name;
end
end
end
metodoDois()
Also, this is just a nitpick, but that code seems a bit un-optimized! I'd recommend using something more like this:
function metodoDois()
print("Write a name: ")
local name = io.read();
print("Write how many times that it will be printed on screen: ")
local quantidade = tonumber(io.read())
for k = 1, quantidade do
io.write(name.." "..k.."\n")
end
end
metodoDois()

Related

Generating all combinations from a table in Lua

I'm trying to iterate through a table with a variable amount of elements and get all possible combinations, only using every element one time. I've landed on the solution below.
arr = {"a","b","c","d","e","f"}
function tablelen(table)
local count = 0
for _ in pairs(table) do
count = count + 1
end
return count
end
function spellsub(table,start,offset)
local str = table[start]
for i = start+offset, (tablelen(table)+1)-(start+offset) do
str = str..","..table[i+1]
end
return str
end
print(spellsub(arr,1,2)) -- Outputs: "a,d,e" correctly
print(spellsub(arr,2,2)) -- Outputs: "b" supposed to be "b,e,f"
I'm still missing some further functions, but I'm getting stuck with my current code. What is it that I'm missing? It prints correctly the first time but not the second?
A solution with a coroutine iterator called recursively:
local wrap, yield = coroutine.wrap, coroutine.yield
-- This function clones the array t and appends the item new to it.
local function append (t, new)
local clone = {}
for _, item in ipairs (t) do
clone [#clone + 1] = item
end
clone [#clone + 1] = new
return clone
end
--[[
Yields combinations of non-repeating items of tbl.
tbl is the source of items,
sub is a combination of items that all yielded combination ought to contain,
min it the minimum key of items that can be added to yielded combinations.
--]]
local function unique_combinations (tbl, sub, min)
sub = sub or {}
min = min or 1
return wrap (function ()
if #sub > 0 then
yield (sub) -- yield short combination.
end
if #sub < #tbl then
for i = min, #tbl do -- iterate over longer combinations.
for combo in unique_combinations (tbl, append (sub, tbl [i]), i + 1) do
yield (combo)
end
end
end
end)
end
for combo in unique_combinations {'a', 'b', 'c', 'd', 'e', 'f'} do
print (table.concat (combo, ', '))
end
For a tables with consecutive integer keys starting at 1 like yours you can simply use the length operator #. Your tablelen function is superfluous.
Using table as a local variable name shadows Lua's table library. I suggest you use tbl or some other name that does not prevent you from using table's methods.
The issue with your code can be solved by printing some values for debugging:
local arr = {"a","b","c","d","e","f"}
function spellsub(tbl,start,offset)
local str = tbl[start]
print("first str:", str)
print(string.format("loop from %d to %d", start+offset, #tbl+1-(start+offset)))
for i = start+offset, (#tbl+1)-(start+offset) do
print(string.format("tbl[%d]: %s", i+1, tbl[i+1]))
str = str..","..tbl[i+1]
end
return str
end
print(spellsub(arr,1,2)) -- Outputs: "a,d,e" correctly
print(spellsub(arr,2,2)) -- Outputs: "b" supposed to be "b,e,f"
prints:
first str: a
loop from 3 to 4
tbl[4]: d
tbl[5]: e
a,d,e
first str: b
loop from 4 to 3
b
As you see your second loop does not ran as the start value is already greater than the limit value. Hence you only print the first value b
I don't understand how your code is related to what you want to achieve so I'll leave it up to you to fix it.

LUA: Looking for a specific table by its variable

I'm currently starting work on a text adventure game in Lua--no addons, just pure Lua for my first project. In essence, here is my problem; I'm trying to find out how I can do a "reverse lookup" of a table using one of its variables. Here's an example of what I've tried to do:
print("What are you trying to take?")
bag = {}
gold = {name="Gold",ap=3}
x = io.read("*l")
if x == "Gold" then
table.insert(bag,gold)
print("You took the " .. gold.name .. ".")
end
Obviously, writing a line like this with every single object in the game would be very... exhausting--especially since I think I'll be able to use this solution for not just taking items but movement from room to room using a reverse lookup with each room's (x,y) coordinates. Anyone have any ideas on how to make a more flexible system that can find a table by the player typing in one of its variables? Thanks in advance!
-blockchainporter
This doesn't directly answer your question as you asked it, but I think it would serve the purpose of what you are trying to do. I create a table called 'loot' which can hold many objects, and the player can place any of these in their 'bag' by typing the name.
bag = {}
loot = {
{name="Gold", qty=3},
{name="Axe", qty=1},
}
print("What are you trying to take?")
x = io.read("*l")
i = 1
while loot[i] do
if (x == loot[i].name) then
table.insert(bag, table.remove(loot,i))
else
i = i + 1
end
end
For bonus points, you could check 'bag' to see if the player has some of that item already and then just update the quantity...
while loot[i] do
if (x == loot[i].name) then
j, found = 1, nil
while bag[j] do
if (x == bag[j].name) then
found = true
bag[j].qty = bag[j].qty + loot[i].qty
table.remove(loot,i)
end
j = j + 1
end
if (not found) then
table.insert(bag, table.remove(loot,i))
end
else
i = i + 1
end
end
Again, this isn't a 'reverse lookup' solution like you asked for... but I think it is closer to what you are trying to do by letting a user choose to loot something.
My disclaimer is that I don't use IO functions in my own lua usage, so I have to assume that your x = io.read("*l") is correct.
PS. If you only ever want objects to have a name and qty, and never any other properties (like condition, enchantment, or whatever) then you could also simplify my solution by using key/val pairs:
bag = {}
loot = { ["Gold"] = 3, ["Axe"] = 1 }
print("What are you trying to take?")
x = io.read("*l")
for name, qty in pairs(loot) do
if x == name then
bag.name = (bag.name or 0) + qty
loot.name = nil
end
end
I have a few notes to start before I specifically address your question. (I just want to do this before I forget, so please bear with me!)
I recommend printing to the terminal using stderr instead of stdout--the Lua function print uses the latter. When I am writing a Lua script, I often create a C-style function called eprintf to print formatted output to stderr. I implement it like this:
local function eprintf(fmt, ...)
io.stderr:write(string.format(fmt, ...))
return
end
Just be aware that, unlike print, this function does not automatically append a newline character to the output string; to do so, remember to put \n at the end of your fmt string.
Next, it may be useful to define a helper function that calls io.read("*l") to get an entire line of input. In writing some example code to help answer your question, I called my function getline--like the C++ function that has similar behavior--and defined it like this:
local function getline()
local read = tostring(io.read("*l"))
return read
end
If I correctly understand what it is you are trying to do, the player will have an inventory--which you have called bag--and he can put items into it by entering item names into stdin. So, for instance, if the player found a treasure chest with gold, a sword, and a potion in it and he wanted to take the gold, he would type Gold into stdin and it would be placed in his inventory.
Based on what you have so far, it looks like you are using Lua tables to create these items: each table has a name index and another called ap; and, if a player's text input matches an item's name, the player picks that up item.
I would recommend creating an Item class, which you could abstract nicely by placing it in its own script and then loading it as needed with require. This is a very basic Item class module I wrote:
----------------
-- Item class --
----------------
local Item = {__name = "Item"}
Item.__metatable = "metatable"
Item.__index = Item
-- __newindex metamethod.
function Item.__newindex(self, k, v)
local err = string.format(
"type `Item` does not have member `%s`",
tostring(k)
)
return error(err, 2)
end
-- Item constructor
function Item.new(name_in, ap_in)
assert((name_in ~= nil) and (ap_in ~= nil))
local self = {
name = name_in,
ap = ap_in
}
return setmetatable(self, Item)
end
return Item
From there, I wrote a main driver to encapsulate some of the behavior you described in your question. (Yes, I know my Lua code looks more like C.)
#!/usr/bin/lua
-------------
-- Modules --
-------------
local Item = assert(require("Item"))
local function eprintf(fmt, ...)
io.stderr:write(string.format(fmt, ...))
return
end
local function printf(fmt, ...)
io.stdout:write(string.format(fmt, ...))
return
end
local function getline()
local read = tostring(io.read("*l"))
return read
end
local function main(argc, argv)
local gold = Item.new("Gold", 3)
printf("gold.name = %s\ngold.ap = %i\n", gold.name, gold.ap)
return 0
end
main(#arg, arg)
Now, as for the reverse search which you described, at this point all you should have to do is check the user's input against an Item's name. Here it is in the main function:
local function main(argc, argv)
local gold = Item.new("Gold", 3)
local bag = {}
eprintf("What are you trying to take? ")
local input = getline()
if (input == gold.name) then
table.insert(bag, gold)
eprintf("You took the %s.\n", gold.name)
else
eprintf("Unrecognized item `%s`.\n", input)
end
return 0
end
I hope this helps!

How can a Lua function return nil, even if the returned value is not nil inside the function?

I have created a function that (pseudo)randomly creates a table containing numbers. I then loop this function until at least correct result is found. As soon as I've confirmed that at least one such result exists, I stop the function and return the table.
When I create tables containing small values, there are no issues. However, once the random numbers grow to the range of hundreds, the function begins to return nil, even though the table is true the line before I return it.
local sort = table.sort
local random = math.random
local aMin, aMax = 8, 12
local bMin, bMax = 200, 2000
local function compare( a, b )
return a < b
end
local function getNumbers()
local valid = false
local numbers = {}
-- Generate a random length table, containing random number values.
for i = 1, random( aMin, aMax ) do
numbers[i] = random( bMin, bMax )
end
sort( numbers, compare )
-- See if a specific sequence of numbers exist in the table.
for i = 2, #numbers do
if numbers[i-1]+1 == numbers[i] or numbers[i-1] == numbers[i] then
-- Sequence found, so stop.
valid = true
break
end
end
for i = 1, #numbers-1 do
for j = i+1, #numbers do
if numbers[j] % numbers[i] == 0 and numbers[i] ~= 1 then
valid = true
break
end
end
end
if valid then
print( "Within function:", numbers )
return numbers
else
getNumbers()
end
end
local numbers = getNumbers()
print( "Outside function:", numbers )
This function, to my understanding, is supposed to loop infinitely until I find a valid sequence. The only way that the function can even end, according to my code, is if valid is true.
Sometimes, more often than not, with large numbers the function simply outputs a nil value to the outside of the function. What is going on here?
You're just doing getNumbers() to recurse instead of return getNumbers(). This means that if the recursion gets entered, the final returned value will be nil no matter what else happens.
In the else case of the if valid then, you are not returning anything. You only return anything in the valid case. In the else case, a recursive call may return something, but then you ignore that returned value. The print you see is corresponding to the return from the recursive call; it isn't making it out the original call.
You mean to return getNumbers().

What is the alternative for switch statement in Lua language?

I have this piece of code in C++ and i want to know how can i write some codes that replace switch statement in Lua because i face many problems and i need to use this statement.
int choice;
do// loop
{
cout<<"\n >>> The General Menu <<< \n";
cout << endl;
cout<< " press (1) to Add "<<endl;
cout<< " press (2) to Save "<<endl;
cout<< " press (3) to Quit " << endl;
cout<< endl;
cout<< "Enter your choice please (1/2/3): ";
cin>>choice;
switch(choice)
{
case 1:
add();
break;
case 2:
save();
break;
default:
cout<<" The program has been terminated "<<endl;
cout<<" Thank you! \n";
}
} while (choice != 3);
}
The statement has been used inside a do..while loop.
In general, if you want a switch statement in Lua, what you ought to be doing is building a table. For your simple case of choice that could be 1, 2, or fail, a simple if statement with a few conditions is sufficient. For more complex cases, a table of functions should be employed:
local c_tbl =
{
[1] = add,
[2] = save,
}
local func = c_tbl[choice]
if(func) then
func()
else
print " The program has been terminated."
print " Thank you!";
end
You can use lexical scoping to allow the functions in the table to be able to access local variables, just as if the code was written inline.
Try this one (click here to run the script in a Lua compiler), Hope the code is self-explanatory ;-) and
resembles the same pseudo code format..!!
print("enter your choice : ")
mychoice = io.read()
switch = function (choice)
-- accepts both number as well as string
choice = choice and tonumber(choice) or choice -- returns a number if the choic is a number or string.
-- Define your cases
case =
{
[1] = function ( ) -- case 1 :
print("your choice is Number 1 ") -- code block
end, -- break statement
add = function ( ) -- case 'add' :
print("your choice is string add ") -- code block
end, -- break statement
['+'] = function ( ) -- case '+' :
print("your choice is char + ") -- code block
end, -- break statement
default = function ( ) -- default case
print(" your choice is din't match any of those specified cases")
end, -- u cant exclude end hear :-P
}
-- execution section
if case[choice] then
case[choice]()
else
case["default"]()
end
end
-- Now you can use it as a regular function. Tadaaa..!!
switch(mychoice)
Lua:
if choice == 1
then add()
elseif choice == 2
then save()
else print "The program has been terminated\nThank you!"
end
one more version of switcher (without initializing table as variable):
local case=2;
local result=({[1]="case1", [2]="case2", 3="case3"})[case];
print (result); --> case2
While simply creating a table indexed by cases with functions as elements is most probably the fastest approach, there is this solution I've made which IMO has better code readability:
function switch(element)
local Table = {
["Value"] = element,
["DefaultFunction"] = nil,
["Functions"] = {}
}
Table.case = function(testElement, callback)
Table.Functions[testElement] = callback
return Table
end
Table.default = function(callback)
Table.DefaultFunction = callback
return Table
end
Table.process = function()
local Case = Table.Functions[Table.Value]
if Case then
Case()
elseif Table.DefaultFunction then
Table.DefaultFunction()
end
end
return Table
end
Example Use:
switch(Player:GetName())
.case("Kate", function() print("This player's name rhymes with Fate")end)
.case("Tod", function() print("This player's name rhymes with Cod") end)
.default(function() print("This player's name is not Kate or Tod") end)
.process()
I encountered this issue with functions that would take different parameters - something which the other answers don't handle well.
I solved that with anonymous functions.
-- call the relevant execution based on its opcode
local instructions = {
[01] = function () self:perform_add(table.unpack(valargs)) end,
[02] = function () self:perform_multiply(table.unpack(valargs)) end,
[03] = function () self:perform_store_input(outputargs[1]) end,
[04] = function () self:perform_output(valargs[1]) end,
[05] = function () self:perform_jnz(table.unpack(valargs)) end,
[06] = function () self:perform_jz(table.unpack(valargs)) end,
[07] = function () self:perform_less_than(table.unpack(valargs)) end,
[08] = function () self:perform_equals(table.unpack(valargs)) end,
[99] = function () self:perform_exit() end,
}
local instr = instructions[opcode]
if (instr) then
instr()
else
print("No instruction for opcode " .. opcode)
end
The actions I want to take in my different switch cases are all defined as anonymous functions in a table. The keys used (e.g. 08 here) are the values our variable to switch on might assume (opcode here). The default case of the switch statement happens in my else clause. There is no requirement for a break equivalent - but if you want to have one case continue with the next you would have to call it explicitly.
Reply to comment asking for clarification:
You're right that this example is not complete. You can find my usage here when I did adventofcode 2019 day 7. I can try answer your questions but I never touched lua before, and never after. valargs is a table of arguments because different functions here take different numbers of arguments. But that is not necessarily relevant to the question. Basically, I'm just calling functions here.
In my example, self exists because I defined the functions on a local (and did some weird changes as outlined here). The relevant code parts:
-- a "class"
local IntComputer = {}
function IntComputer:perform_exit()
self.program_ended = true
end
function IntComputer:perform_add(a, b, target)
print(" " .. a .. " + " .. b .. " => " .. target)
self:set_value(target, a+b)
end
If you want switch as a function that is callable, you could use something funny with the callback feature:
(The example below is a switch statement based on the variable type, but you could make the table index into whatever you want to test it for. Just change the return statement of the switch function to not test for type(case))
(This is essentially a lazy table lookup much like Python's dictionary feature but each element is a function)
#!/usr/bin/lua
-- Callback switch statement:
local function switch(a, case)
-- Local variable instead of function(a) on every case:
local value = a
-- Cases list:
local switchcase = {}
-- Cases:
switchcase["string"] = function()
return (tostring(value) .. " is a string")
end
switchcase["number"] = function()
return tostring(value .. " is a number")
end
switchcase["boolean"] = function()
return (tostring(avalue) .. " is a boolean")
end
return switchcase[type(case)](a)
end
local value = 5
print(switch(value,value)) --> 5 is a number
local value = "test"
print(switch(value,value)) --> test is a string
local value = true
print(switch(value,value)) --> true is a boolean
I don't know the performance of this code compared to the two answers given above, but using local variables ought to make it quick enough for repeated use. If you make your switch function in the global scope it could become a standard function for your project to be used.
Here's another fun method using loadstring() and a table lookup.
switch = function(cases,args)
if (cases[args] == nil) then return args else return assert(loadstring ('return ' .. cases[args]))() end
end
local case = 2
local result = switch({
[1] = "2^" .. case,
[2] = string.format("2^%i",case),
[3] = tostring(2^case)
},
case
)
print(result) --> 4
This method is somewhat dangerous to use since loadstring() is similar to Python's eval() function.
I found it ugly to write "function(x)" on every case in the examples provided by the Lua wiki. This is a neat way.
The "default" case is the "return args" part of the function.
I use this code :
while true do local tmpswitch1 = exp ; --[[ switch <exp> do ]]
if tmpswitch1 == exp1 then --[[ case <exp1> : ]]
-- do something
break
end ;if tmpswitch1 == exp2 then --[[ case <exp2> : ]]
-- do something
break
end ; --[[ default : ]]
-- do something
break ; end --[[ switch tmpswitch1 ]]
function case(i,d) return function(t) return t[i] or d end end
x='two'
r=case(x) {
one=1,
two=2,
three=3,
}
case(r,function() print "default" end) {
[1]=function() print "one" end,
[2]=function() print "two" end,
[3]=function() print "three" end,
}()

lua Hashtables, table index is nil?

What I'm currently trying to do is make a table of email addresses (as keys) that hold person_records (as values). Where the person_record holds 6 or so things in it. The problem I'm getting is that when I try to assign the email address as a key to a table it complains and says table index is nil... This is what I have so far:
random_record = split(line, ",")
person_record = {first_name = random_record[1], last_name = random_record[2], email_address = random_record[3], street_address = random_record[4], city = random_record[5], state = random_record[6]}
email_table[person_record.email_address] = person_record
I wrote my own split function that basically takes a line of input and pulls out the 6 comma seperated values and stores them in a table (random_record)
I get an error when I try to say email_table[person_record.email_address] = person_record.
But when I print out person_record.email_address it's NOT nil, it prints out the string I stored in it.. I'm so confused.
function split(str, pat)
local t = {} -- NOTE: use {n = 0} in Lua-5.0
local fpat = "(.-)" .. pat
local last_end = 1
local s, e, cap = str:find(fpat, 1)
while s do
if s ~= 1 or cap ~= "" then
table.insert(t,cap)
end
last_end = e+1
s, e, cap = str:find(fpat, last_end)
end
if last_end <= #str then
cap = str:sub(last_end)
table.insert(t, cap)
end
return t
end
The following code is copy and pasted from your example and runs just fine:
email_table = {}
random_record = {"first", "second", "third"}
person_record = {first_name = random_record[1], last_name = random_record[1], email_address = random_record[1]}
email_table[person_record.email_address] = person_record
So your problem is in your split function.
BTW, Lua doesn't have "hashtables". It simply has "tables" which store key/value pairs. Whether these happen to use hashes or not is an implementation detail.
It looks like you iterating over some lines that have comma-separated data.
Looking at your split function, it stops as soon as there's no more separator (,) symbols in particular line to find. So feeding it anything with less than 3 ,-separated fields (for very common example: an empty line at end of file) will produce a table that doesn't go up to [3]. Addressing any empty table value will return you a nil, so person_record.email_address will be set to nil as well on the 2nd line of your code. Then, when you attempt to use this nil stored in person_record.email_address as an index to email_table in 3rd line, you will get the exact error you've mentioned.

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