i want to do something like ..
if mark is between 80-100 it will show A+
if mark is between 70-79 it will show A
etc

I want to do it with “case in esac” not with if-elif-fi

But how do I do complex expression in case 

```
echo “enter mark”
read mark
case $mark in
(( mark>=80 && mark<=100 ))) echo “A+”
..
..
..
esac

```

i tried this. it is easy with if-elif-fi but what i should do in the 'case'
thank you.