How to loop through array in batch?

Another Alternative using defined and a loop that doesn't require delayed expansion:

set Arr[0]=apple
set Arr[1]=banana
set Arr[2]=cherry
set Arr[3]=donut

set "x=0"

:SymLoop
if defined Arr[%x%] (
    call echo %%Arr[%x%]%%
    set /a "x+=1"
    GOTO :SymLoop
)

Be sure you use "call echo" as echo won't work unless you have delayedexpansion and use ! instead of %%

If you don't know how many elements the array have (that seems is the case), you may use this method:

for /F "tokens=2 delims==" %%s in ('set sources[') do echo %%s

Note that the elements will be processed in alphabetical order, that is, if you have more than 9 (or 99, etc) elements, the index must have left zero(s) in elements 1..9 (or 1..99, etc.)