Scientific Calculator Using awk Command in Linux

pi=`echo "scale=10;4*a(1)" | bc -l`

while true
do

cat << MENU

      Menu:
    a) Floating Point Calculations
    b) Trigonometric Operations
    c) Logarithmic Operations
    d) Exponential Operations
    
MENU
echo '
Enter your Choice: \c'
read choice

case $choice in
    
    a)  echo "\nEnter expression: "
        read exp    
        cal()
            awk "BEGIN{print $*}";    
        echo "Answer: " `cal $exp`
        ;;

    b)  echo "\nEnter Trigonometric function : "
            read exp
            echo "Degree: "
            read degree

         e=$(awk "BEGIN{print $exp($degree*atan2(0,-1)/180)}")
            echo "
            $exp($degree)= $e" 
            ;;

        c)  echo "\nEnter the logarithmic value: "
            read value
            echo $value | awk '{printf "%11.9f\n",log($1)/log(10)}' 
            ;;

        d)  echo "\nEnter the base number x: "    
        read x
        echo "Enter exponent number y: "
        read y
        E=$(echo "$x 1" | awk "{print (($x/1)^$y)}")
        echo "$x^$y = $E"     
            ;;            
        *)
              break;;    
          *)
              break;;
esac
done