Make a Student Marksheet in Linux Shell Scripts

echo "Enter Student Number:->";
read no
echo "Enter Student Name:->";
read name

echo "Enter First Subject Marks:->";
read s1
echo "Enter Second Subject Marks:->";
read s2
echo "Enter Third Subject Marks:->";
read s3

    echo "1:Display Grade";
    echo "2:Display Persentage";
    echo "3:Display Total";
    echo "0:Exit";

while((1))
do
   
    echo "Please Enter Above Option:->";
    read c
    tot=`expr $s1 + $s2 + $s3`;
    per=$(echo " scale =3; $tot/3 " |bc)
    a=$(echo " $tot/3 " |bc)

    case $c in
        1)
            if test $a -ge 70
            then
                echo "Grade:->Distiction";
            elif test $a -ge 60
            then   
                echo "Grade:->First Class";
            elif test $a -ge 50
            then
                echo "Grade:->Second Class";   
            elif test $a -ge 40
            then
                echo "Grade:->Pass class";
            else
                echo "Grade:->Fail";
            fi



            ;;
         2)echo "Persentage:->" $per
            ;;
        3) echo "Total Is:->"$tot
            ;;
        0) exit
            ;;

        *) echo "Please Select Valid Option";
    esac

done