Boolean chain

Leap
Leap in Tcl 
expr {$year % 4 == 0 && ($year % 100 != 0 || $year % 400 == 0)}

The Boolean expression $year % 4 == 0 checks the remainder from dividing $year by 4. If a year is evenly divisible by 4, the remainder will be zero. All leap years are divisible by 4, and this pattern is then repeated whether a year is not divisible by 100 and whether it is divisible by 400.

Parentheses are used to control the order of precedence: logical AND && has a higher precedence than logical OR ||.

year divisible by 4 not divisible by 100 divisible by 400 result
2020 true true not evaluated true
2019 false not evaluated not evaluated false
2000 true false true true
1900 true false false false

By situationally skipping some of the tests, we can efficiently calculate the result with fewer operations.

6th Nov 2024 · Found it useful?

Other Approaches to Leap in Tcl

Other ways our community solved this exercise
expr {$year % 100 == 0 ? $year % 400 == 0 : $year % 4 == 0}
Ternary operator

Use a ternary operator of Boolean expressions. 

set timestamp [clock scan "$year-02-28" -format {%Y-%m-%d}]
set next_day [clock add $timestamp 1 day]
set day [clock format $next_day -format {%d}]
expr {$day == 29}
Clock command

Use the clock command to do date addition.