Shell Script for Calculator

n=$#
echo "1.addition"
echo "2.subtraction"
echo "3.multiplication"
echo "4.division"
echo "5.Mod"
echo "enter the choice of operation:-"
read c
echo "Enter two number for Arithmatic Operation"
read a
read b
case $c in
1)
add=`expr $a + $b`
echo "addition of number is:- $add"
;;
2)
sub=`expr $a - $b`
echo "subtraction of number is:- $sub"
;;
3)
mult=`expr $a \* $b`
echo "multiplication of number is:- $mult"
;;
4)
div=`expr $a / $b`
echo "division of number is:- $div"
;;
5)
mod=`expr $a % $b`
echo "Mode is $mod"
*)
echo "wrong input"
;;
esac