Range Checking

If you wish to check that a variable’s value is in range, you could do it like this:

if (number >= 0 && number <= 100) {
    // use number
}
else {
    // do something else
}

An alternative approach in Kotlin is to define a range and check for membership of that. The above example could be rewritten to use a range like this:

if (number in 0..100) {
    // use number
}
else {
    // do something else
}

Here, 0..100 defines a closed integer range, with 0 and 100 included as endpoints.

Ranges are not limited to integers. You can also define floating point ranges, ranges of characters, even ranges of strings:

0.0..100.0
'a'..'z'
"aaa".."zzz"

To understand that last example, think of an alphabetical ordering of strings, much like words in an English dictionary. Testing whether a string is in the range "aaa".."zzz" will yield a result of false if that string would come before aaa or after zzz in such a dictionary; otherwise, it will yield a result of true.

In each of the examples above, literals have been used as the endpoints, but keep in mind that you are also allowed to use variables as endpoints of a range.

Task 4.2

Write a program to simulate ordering a pizza.

• Your program should be in a file named Pizza.kt, in the tasks/task4_2 subdirectory of your repository.

• Your program should present a menu to the user consisting of four pizza options. It should label these options a, b, c and d.

• Your program should use readln().lowercase() to read the user’s input and convert it to a lowercase string.

• Your program should use an if expression to check that the length of the input string is 1, and that the first (and only) character of the string is one of the four available pizza options. It should use a Char range for the latter.

• If the input is valid, your program should print “Order accepted”; otherwise, it should print “Invalid choice!”

Here’s an example of program output and user input:

PIZZA MENU

(a) Margherita
(b) Quattro Stagioni
(c) Seafood
(d) Hawaiian

Choose your pizza (a-d): b
Order accepted