storing values in a list or array

Shell Programming and Scripting
1

i have a file called file.txt having the following entries.
2321
2311
2313
4213

i wnat to store these values in a list and i want to iterate the list using loop and store it in another list

2 
i=0;
while read line; 
do a[$i]=$line;
echo ${a[$i]};
i=$(( i+1 )); 
done <file

for (( j=0;j<= ${#a[@]};j++));
do 
b[$j]=${a[$j]};
echo ${b[$j]}; 
done

cheers,
Devaraj Takhellambam