add()
{
a=`expr $1 + $2`
echo "Result is $a"
}
sub()
{
b=`expr $1 - $2`
echo "Result is $b"
}
mul()
{
a=`expr $1 \* $2`
echo "Result is $a"
}
div()
{
a=`expr $1 / $2`
echo "Result is $a"
}
fac()
{
x=1
y=$1
if test $y -eq 0
then
echo "Result is 1"
else
while [ $y -gt 0 ]
do
x=`expr $x \* $y`
y=`expr $y - 1`
done
echo "Result is $x"
fi
}
pow4()
{
a=`expr $1 \* $1 \* $1 \* $1`
echo "Result is $a"
}
while :
do

 echo -e "MAIN MENU \n"
 echo "1.add"
 echo "2.sub"
 echo "3.mul"
 echo "4.div"
 echo "5.fac"
 echo "6.power4"
 echo "7.exit"
 echo -n "Enter your choice :"
 read ch
 echo $ch
case $ch in
 1)echo "Enter two numbers"
   read a b
   add $a $b;;
2) echo "Enter two numbers"
   read a b
   sub $a $b;;
3) echo "Enter two numbers"
   read a b
   mul $a $b;;
4) echo "Enter two numbers"
   read a b
   div $a $b;;
5) echo "Enter a number"
   read a
   fac $a;;
6) echo "Enter a number"
   read a
   pow4 $a;;
7) exit 0;;
*) echo "Wrong choice";;
esac
done