Think Perl 6

Chapter 4. Loops, Conditionals, and Recursion

The main topic of this chapter is the if statement, which executes different code depending on the state of the program. But first I want to introduce two new operators: integer division and modulo.

Integer Division and Modulo

The integer division operator, div, divides two numbers and rounds down to an integer. For example, suppose the runtime of a movie is 105 minutes. You might want to know how long that is in hours. In Perl, conventional division returns a rational number (in many languages, it returns a floating-point number, which is another kind of internal representation for noninteger numbers):

> my $minutes = 105;
> $minutes / 60;
1.75

But we don’t normally write hours with decimal points. Integer division returns the integer number of hours, dropping the fraction part:

> my $minutes = 105;
> my $hours = $minutes div 60;
1

In arithmetic, integer division is sometimes called Euclidean division, which computes a quotient and a remainder.

To get the remainder, you could subtract off one hour in minutes:

> my $remainder = $minutes - $hours * 60;
45

An alternative is to use the modulo operator, %, which divides two numbers and returns the remainder:

> my $remainder = minutes % 60;
45

The modulo operator is very common in programming languages and is more useful than it seems. For example, you can check whether one number is divisible by another—if $dividend % $divisor is zero, then $dividend is divisible by $divisor. This is commonly ...