Course of Raku / Essentials / Loops / Exercises / Factorial

Solution: Factorial

A factorial of N is a product of integer numbers from 1 to and including N. E.g., factorial of 4 is 1 * 2 * 3 * 4 = 24.

Code

my $n = 8;

my $f = 1;
$f *= $_ for 2..$n;

say $f;

🦋 Find the program in the file factorial.raku.

Output

Run the program a few times and try different values of $n.

$ raku exercises/loops/factorial.raku
40320

Comments

This program uses the *= operator, which is a shortcut for multiplication with the assignment: $x *= $y is equivalent to $x = $x * $y.

You can use a ’full‘ loop instead of a postfix form:

my $n = 8;

my $f = 1;
for 2..$n -> $x {
    $f *= $x;
}

say $f;

More on this subject

We will return to this task a number of times. In this part of the course, we will also solve this problem recursively.

In the second part of the course, we will learn about the so-called reduction operators, which make the solution trivial. Also, there will be a way to define a custom operator ! so that you can write $n! to compute a factorial. Finally, there will be another chance to see an interesting solution when we’ll talk about the where clause.

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