Names for values - TorbScript

A value is a piece of information: a word, a number. When a program needs the same value more than once, it gives the value a name and uses the name from then on.

const name = "Ada" means: from now on, name stands for "Ada". Inside text, a name in curly braces is replaced by its value, so "Hello, {name}!" becomes Hello, Ada!.

const name = "Ada"
print "Hello, {name}!"
print "Goodbye, {name}!"
// prints Hello, Ada!
// prints Goodbye, Ada!

A name whose value changes#

const means the value stays the same for good. When the value has to change - a score, a counter - write var instead, and give the name a new value with =.

score = score + 10 reads: take the value of score, add 10, and make that the new value of score.

var score = 0
score = score + 10
score = score + 5
print "Score: {score}"
// prints Score: 15

What happens if you change a const?

The program does not run. The computer checks the whole program before it runs a single line, and tells you where the mistake is:

Does not compile

const name = "Ada"
name = "Alan"
print name
// error: `name` is a `const`. Only a `var` binding can be changed

That check is a good thing: a value you said stays the same really does. A name for a value is called a binding, which is the word the error uses.

Exercise#

You have 3 coins and find 4 more. Add one line so the program prints Coins: 7.

var coins = 3
print "Coins: {coins}"

Expected output

Coins: 7

Run it on your computer: torb run names-for-values.trb

Hint

Before the print line, give coins a new value: its old value plus 4.

Solution

var coins = 3
coins = coins + 4
print "Coins: {coins}"
// prints Coins: 7

Recap#

const gives a value a name that never changes, var one that can, and {name} puts a value into text.