Shell Script for simple calculator to perform addition subtraction multiplication and division based on the symbol using case statements

Program

echo "Enter the first number" 
read a
echo "Enter the second number" 
read b
echo "Enter the operator:"
echo -e "Addition: +\nSubtraction: -\nMultiplication: x\nDivision: /"
read op
	case $op in
	 +) c=`expr $a + $b`
		echo "Sum of $a and $b is $c";;
	 -) c=`expr $a - $b`
            echo "Difference of $a and $b is $c";;
	 x) c=`expr $a \* $b`
            echo "Product of $a and $b is $c";;
	 /) c=`expr $a / $b`
            echo "Division of $a and $b is $c";;
	 *) echo "Invalid Operator"
	    exit;;
	esac

Output 1

$ chmod 755 calculator-using-case.sh
$ sh calculator-using-case.sh
Enter the first number
7
Enter the second number
9
Enter the operator:
Addition: +
Subtraction: -
Multiplication: x
Division: /
+
Sum of 7 and 9 is 16

Output 2

$ sh calculator-using-case.sh
Enter the first number
6
Enter the second number
12
Enter the operator:
Addition: +
Subtraction: -
Multiplication: x
Division: /
-
Difference of 6 and 12 is -6

Output 3

$ sh calculator-using-case.sh
Enter the first number
5
Enter the second number
3
Enter the operator:
Addition: +
Subtraction: -
Multiplication: x
Division: /
x 
Product of 5 and 3 is 15

Output 4

$ sh calculator-using-case.sh
Enter the first number
99
Enter the second number
3
Enter the operator:
Addition: +
Subtraction: -
Multiplication: x
Division: /
/
Division of 99 and 3 is 33

Output 5

$ sh calculator-using-case.sh
Enter the first number
6
Enter the second number
7
Enter the operator:
Addition: +
Subtraction: -
Multiplication: x
Division: /
%
Invalid Operator