When you pipe into a while
loop in Bash, it creates a subshell. When the subshell exits, all variables return to their previous values (which may be null or unset). This can be prevented by using process substitution.
LONGEST_CNT=0
while read -r line
do
line_length=${#line}
if (( line_length > LONGEST_CNT ))
then
LONGEST_CNT=$line_length
LONGEST_STR=$line
fi
done < <(find samples/ ) # process substitution
echo $LONGEST_CNT : $LONGEST_STR