Shell program for calculating area of circle

echo -n "Enter the radius of a circle : "
read r

# use formula to get it d is diameter
d=$(echo "scale=2;2 * $r"|bc)
circumference=$(echo "scale=2;3.14 * $d"| bc)

# use formula to get it
area=$(echo "scale=2;3.14 * ($r * $r)" | bc)

echo "Circumference of circle is $circumference"
echo "Area of circle is $area"