A
for
loop consists of three parts: the initializer (
roll = 0
), the condition (
roll <
3
), and the
final expression (
roll++
). It’s nothing that can’t be constructed with a
while
loop, but it conveniently puts all the loop information in one place. Here’s how
it looks in JavaScript:
const
hand
=
[];
for
(
let
roll
=
0
;
roll
<
3
;
roll
++
) {
hand
.
push
(
randFace
());
}
Programmers have a tendency to count from 0, which is why we start at roll 0 and
stop at roll 2.
It has become a convention to use the variable i (shorthand for
“index”) in a for loop, no matter what you’re counting, though you
can use whatever variable name you wish. I chose roll here to be
clear that we’re counting the number of rolls, but I had to catch
myself: when I first wrote out this example, I used i out of habit!
if Statement
We’re almost there! We’ve placed our bets and rolled our hand; all that’s left is to col‐
lect any winnings. We have three random faces in the
hand
array, so we’ll use another
for
loop to see if any of them are winners. To do that, we’ll use an
if
statement (this
time without an
else
clause). Our final flowchart is shown in
Notice the difference between an
if...else
statement and an
if
statement: only one
of the
if
statement’s branches lead to an action, whereas both of the
if...else
state‐
ment’s do. We translate this into code for the final piece of the puzzle:
let
winnings
=
0
;
for
(
let
die
=
0
;
die
<
hand
.
length
;
die
++
) {
let
face
=
hand
[
die
];
if
(
bets
[
face
]
>
0
)
winnings
=
winnings
+
bets
[
face
];
}
funds
=
funds
+
winnings
;
Note that, instead of counting to 3 in the
for
loop, we count to
hand.length
(which
happens to be 3). The goal of this part of the program is to calculate the winnings for
any hand. While the rules of the game call for a hand of three dice, the rules could
change…or perhaps more dice are given as a bonus, or fewer dice are given as a pen‐
alty. The point is, it costs us very little to make this code more generic. If we change
the rules to allow more or fewer dice in a hand, we don’t have to worry about chang‐
ing this code: it will do the correct thing no matter how many dice there are in the
hand.
A Control Flow Primer | 65
