(UNIX and Linux bash script question)

Explain what each line in the following script does(write after #):

typeset -i X I=0 #

while read X ; do #

A[I]=$X #

(( ++I )) #

done #

B=( $(for C in ${A[*]} ; do echo $C ; done | sort -n) ) #

D=${#A[*]} #

if (( D%2 == 1 )) ; then #

echo ${B[D/2]} #

else #

echo $(( (B[D/2] + B[D/2-1]) / 2 )) #

fi #