Could someone tell me why in the following code, when it iterates on the
array ‘arraya’ it skips the first position? It is strange because
immediatley before each is called on arraya, I call inspect and you can
clearly see the first value is 1800, but the first value out put is
1801.
#code start
startyear = nil
endyear = nil
arraya = []
currentyearis = false
puts ‘What year should I start with?’
startyear = gets.chomp
puts ‘What year should I end with?’
endyear = gets.chomp
#assign years including and between start/endyear into array
arraya = (startyear…endyear).to_a
#iterate on array
puts arraya.inspect
arraya.each do |currentyear|
if currentyear.to_i % 4 == 0
if currentyear.to_i % 100 == 0
puts currentyear.inspect
puts(‘The Year ’ + currentyear + ’ is not a leap year.’) if
currentyear.to_i % 400 == 0
else
puts(‘The Year ’ + currentyear + ’ is a leap year.’)
end
else
puts(‘The Year ’ + currentyear + ’ is not a leap year’)
end
end
#code end
On Fri, Jan 28, 2011 at 4:26 PM, Chris R. [email protected]
wrote:
Could someone tell me why in the following code, when it iterates on the
array ‘arraya’ it skips the first position?
Does it?
It is strange because
immediatley before each is called on arraya, I call inspect and you can
clearly see the first value is 1800, but the first value out put is
1801.
#code start
startyear = nil
endyear = nil
These assignments are superfluous.
arraya = (startyear…endyear).to_a
You do not do any checking on the input so you might get a sequence
that you do not expect.
#iterate on array
puts arraya.inspect
arraya.each do |currentyear|
if currentyear.to_i % 4 == 0
if currentyear.to_i % 100 == 0
puts currentyear.inspect
You probably think somthing is omitted because the line above is
guarded by a condition. You probably rather want to move this line up
directly behind #each.
#code end
Kind regards
robert
The answer is that your code doesn’t take into account the situation
where
the year is divisible by 4 and 100, but not divisible by 400:
[1800 % 4, 1800 % 100, 1800 % 400]
=> [0, 0, 200]
As a suggestion, you might want to make your range of years a range of
numbers, to prevent having to call to_i on them when using %. You can
use
interpolated strings and Ruby will convert the numbers to a string for
you.
Here’s a re-indented, neatened up (in my opinion, anyway) version of
your
code:
puts “What year should I start with?”
start_year = 1800 # gets.chomp.to_i
puts “What year should I end with?”
end_year = 1900 # gets.chomp.to_i
years = (start_year…end_year)
years.each do |year|
if year % 4 == 0
if year % 100 == 0
puts “#{year} is not a leap year.” if year % 400 == 0
else
puts “#{year} is a leap year.”
end
else
puts “#{year} is not a leap year.”
end
end
As a naive way of finding bugs like this, you can insert lines to print
what’s going on inside your iteration. I’ve highlighted the debug lines
with
comments, to point out the additions.
years.each do |year|
puts “Working on #{year}” #debug
if year % 4 == 0
puts “Divisible by 4” #debug
if year % 100 == 0
puts “Divisible by 100” #debug
puts “#{year} is not a leap year.” if year % 400 == 0
else
puts “Not divisible by 100” #debug
puts “#{year} is a leap year.”
end
else
puts “Not divisible by 4” #debug
puts “#{year} is not a leap year.”
end
end
Checking the output of executing this will show you something is
missing:
Working on 1800
Divisible by 4
Divisible by 100
Working on 1801
Not divisible by 4
1801 is not a leap year.
Working on 1802
Hopefully this is useful.
On Fri, Jan 28, 2011 at 3:43 PM, Robert K.
[email protected]wrote:
These assignments are superfluous.
This was something else I was going to point out. You don’t have to
“initialize” your local variables like this with “empty” values.