Write a shell script of calculator which performs Addition , Subtract ,Division ,Multiplication using while loop and switch statement - OS

i="y"
while [ $i = "y" ]
do
echo " Enter one no."
read n1
echo "Enter second no."
read n2
echo "1.Addition"
echo "2.Subtraction"
echo "3.Multiplication"
echo "4.Division"
echo "Enter your choice"
read ch
case $ch in
1)sum=`expr $n1 + $n2`
echo "Sum ="$sum;;
2)sum=`expr $n1 - $n2`
echo "Sub = "$sum;;
3)sum=`expr $n1 \* $n2`
echo "Mul = "$sum;;
4)sum=`expr $n1 / $n2`
echo "Div = "$sum;;
*)echo "Invalid choice";;
esac
echo "Do u want to continue ? y/n"
read i
if [ $i != "y" ]
then
exit
fi
done