Can you please assist me to debug the following errors i am having with my very first Lua program and let me know you are to successfully compile this program on your side?

i would greatly appreciate any help and assistance you can provide me with to correct the below issues.

lua: exam.lua:$70$: attempt to index field $\text{'}?\text{'}($a nil value$)$

stack traceback:

exam.lua:$70$: in main chunk

$[$C$]$: $?$

lua: main.lua:$78$: attempt to index field $\text{'}?\text{'}($a nil value$)$

stack traceback:

main.lua:$78$: in main chunk

$[$C$]$: $?$

lua: exam.lua:$90$: attempt to index local 'city' $($a number value$)$

stack traceback:

exam.lua:$90$: in main chunk

$[$C$]$: $?$

lua: exam.lua:$96$: attempt to index field $\text{'}?\text{'}($a nil value$)$

stack traceback:

exam.lua:$96$: in main chunk

$[$C$]$: $?$

lua: exam.lua:$104$: attempt to call global 'match' $($a nil value$)$

stack traceback:

exam.lua:$104$: in main chunk

$[$C$]$: $?$

$---$

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

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

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

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

$--$

end

function mostconnected$($grid$)$

$--$

end

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

while true do

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

if command $==$ "areneighnours" 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 total$\_$distance $=0$

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

while city $>=0$ do

total$\_$distance $=$ total$\_$distance $+$ grid$[$city$][$city $+1]$

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

end

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

elseif command $==$ "listneighbours" then

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

local neighbour $=\{\}$

for i $=0,$ #grid $-1$ do

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

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

end

end

table.sort$($neighbours$)--$ in ascending order

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

print$($neighbour$)$

end

elseif command $==$ "largestdistance" then

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

local largest$\_$distance $=0$

for i $=0,$ #grid $-1$ do

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

end

elseif command $==$ "isvalid" then

local is$\_$symmetric $=$ true

for i $=0,$ #grid $-1$ do

for j $=$ i $+1,$#grid $-1$ do

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

is$\_$symmetric $=$ false

break

end

end

end

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

elseif command $==$ "pathsfromto" then

local startcity $,$ endcity $=$ tonumber$($io$.$read$($match$("(\%$S$+)\%$s$*(\%$S$+)")))$

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

elseif command $==$ "mostconnected" then

mostconnected$($grid$)$

print$($mostconnected$)$

elseif command $==$ "exit" then

break

end

end