i followed your suggestions but down to two sets of errors left, are you able to assist?

i followed all your advice and even used a text comparator but still have these two issues,can you please check to see if i am missing something in my Lua progran source code

lua: main.lua:$54$: attempt to get length of field $\text{'}?\text{'}($a nil value$)$

stack traceback:

main.lua:$54$: in function 'listneighbours'

main.lua:$127$: in main chunk

$[$C$]$: $?$

lua: main.lua:$68$: attempt to get length of field $\text{'}?\text{'}($a nil value$)$

stack traceback:

main.lua:$68$: in function 'largestdistance'

$--$load a grid from a file

function loadgrid$($filename$)$

local file $=$ io$.$open$($filename$,"$r$")$

if not file then

print$("$Error: Unable to open file"$)$

return

end

local grid $=\{\}$

for line in file:lines$()$ do

local row $=\{\}$

for num in line:gmatch$("\%$S$+")$ do

table.insert$($row$,$ tonumber$($num$))$

end

table.insert$($grid$,$ row$)$

end

file:close$()$

return grid

end

$--$check to see if they are neighbouring cities

function areneighbours$($city$1,$ city$2,$ grid$)$

if city$1>=0$ and city$1<$ #grid and city$2>=0$ and city$2<$ #grid$[$city$1+1]$ then

return grid$[$city$1+1][$city$2+1]>0$

else

return false

end

end

$--$check to see if it forms a path

function ispath$($grid$,$ cities$)$

for i $=1,$ #cities $-1$ do

if grid$[$cities$[$i$]][$cities$[$i $+1]]==0$ then

return false

end

end

return true

end

$--$determine the distance of a path

function pathlength$($grid$,$ cities$)$

local total$\_$distance $=0$

for i $=1,$ #cities $-1$ do

total$\_$distance $=$ total$\_$distance $+$ grid$[$cities$][$i$][$cities$[$i $+1]]$

end

print$($total$\_$distance$)$

end

$--$find the neighbour of a given city

function listneighbours$($city $,$ grid$)$

local neighbours $=\{\}$

for i $=1,$ #grid$[$city$]$ do

if grid$[$city$][$i$]$ ~$=0$ then

table.insert$($neighbours$,$ i $-1)$

end

end

table.sort$($neighbours$)$

for $\_,$ neighbour in ipairs$($neighbours$)$ do

print$($neighbour$)$

end

end

$--$determine largest distance from a city

function largestdistance$($city$,$ grid$)$

local largest$\_$distance $=0$

for i $=1,$ #grid$[$city$]$ do

largest$\_$distance $=$ math.max$($largest$\_$distance, grid$[$city$][$i$])$

end

print$($largest$\_$distance$)$

end

$--$check to see if grid is symmetrical

function isvalid$($grid$)$

local is$\_$symmetric $=$ true

for i $=1,$ #grid do

for j $=$ i $+1,$ #grid$[$i$]$ do

if grid$[$i$][$j$]$ ~$=$ grid$[$j$][$i$]$ then

is$\_$symmetric $=$ false

break

end

end

end

print$($is$\_$symmetric and "Yes" or $"$No$")$

end

$--$functin to find paths from one city to another

function pathsfromto$($startcity$,$ endcity, grid$)$

$--$

end

$--$function to find the most connected city

function mostconnected$($grid$)$

$--$

end

$--$main program

local grid $=$ loadgrid$("$grid$.$txt$")$

while true do

local command $=$ io$.$read$("*$line$")$

if command $==$ "areneighbours" then

local city$1,$ city$2=$ io$.$read$("*$n$","*$n$")$

local result $=$ areneighbours$($city$1,$ city$2,$ grid$)$ and "Yes" or $"$No$"$

print$($result$)$

elseif command $==$ "ispath" then

local cities $=\{\}$

for city in io$.$read$()$:gmatch$("\%$S$+")$ do

table.insert$($cities$,$ tonumber$($city$))$

end

if ispath$($grid$,$ cities$)$ then

print$("$Yes$")$

else

print$("$No$")$

end

elseif command $==$ "pathlength" then

local cities $=\{\}$

for city in io$.$read$()$:gmatch$("\%$S$+")$ do

table.insert$($cities$,$ tonumber$($city$))$

end

pathlength$($grid$,$ cities$)$

elseif command $==$ "listneighbours" then

local city $=$ tonumber$($io$.$read$("*$number$"))$

listneighbours$($city$,$ grid$)$

elseif command $==$ "largestdistance" then

local city $=$ tonumber$($io$.$read$("*$number$"))$

largestdistance$($city$,$ grid$)$

elseif command $==$ "isvalid" then

isvalid$($grid$)$

elseif command $==$ "pathsfromto" then

local startcity, endcity $=$ string.match$($io$.$read$("*$line$"),"(\%$d$+)\%$s$+(\%$d$+)")$

pathsfromto$($tonumber$($startcity$),$ tonumber$($endcity$),$ grid$)$

elseif command $==$ "mostconnected" then

mostconnected$($grid$)$

elseif command $==$ "exit" then

break

end

end