Course of Raku / Essentials / Control flow essentials / Conditional checks / Exercises / Leap year

Solution: Leap year

Disclaimer

The solution shown below aims to train you using conditional checks. In real life, you can learn the methods of the built-in Date class. We will learn it in the second part of the course.

Solution

The algorithm of the detection if a year is leap:

1. if year is not divisible by 4 => common year
2. if year is not divisible by 100 => leap year
3. if year is not divisible by 400 => common year
4. else => leap year

Note that you can use the built-in types for working with date and time, so we’ll return to this task in the second part of the course.

Code 1

The first solution reproduces the above steps literally:

my $year = prompt 'Year: ';

if $year % 4 {
    say 'Common year';
}
elsif $year % 100 {
    say 'Leap year';
}
elsif $year % 400 {
    say 'Common year';
}
else {
    say 'Leap year';
}

🦋 Find the program in the file leap-year.raku.

Code 2

In the second solution, the logic is packed to a single expression. Parentheses are not always needed but added here for clarity.

my $year = prompt 'Year: ';

say (($year %% 400) || (($year %% 4) && ($year % 100))) ?? 'Leap year' !! 'Common year';

🦋 Find the program in the file leap-year-formula.raku.

Output

Try both programs with the most critical cases, for example, 1900, 2000, 2020, 2021.

$ raku exercises/conditional-checks/leap-year.raku
Year: 1900
Common year

$ raku exercises/conditional-checks/leap-year.raku
Year: 2000
Leap year

$ raku exercises/conditional-checks/leap-year-formula.raku
Year: 2020
Leap year

$ raku exercises/conditional-checks/leap-year-formula.raku
Year: 2021
Common year

%%tipblock ## %% vs %

Note that in Boolean contexts, the %% and % operators are complementary. You can use this fact to choose one of the operators to avoid explicit comparison with zero.

CodeBlockPlaceholder5 %%/tipblock

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