How to write shell script that will add two nos, which are supplied as command line argument, and if this two nos are not given show error and its usage

<code>
#!/bin/bash
#
# Linux Shell Scripting Tutorial 1.05r3, Summer-2002
#
# Written by Vivek G. Gite < This e-mail address is being protected from spambots. You need JavaScript enabled to view it >
#
# Latest version can be found at www.nixcraft.com/
#
# Q1.Script to sum to nos
#

if [ $# -ne 2 ]
then
echo "Usage - $0 x y"
echo " Where x and y are two nos for which I will print sum"
exit 1
fi
echo "Sum of $1 and $2 is `expr $1 + $2`"
#
# ./ch.sh: vivek-tech.com to nixcraft.com referance converted using this tool
# See the tool at www.nixcraft.com/uniqlinuxfeatures/tools/
#

</code>