Hey All!
Now that we
have an idea of how to use If statements
in our code, let’s look at how we might use multiple If statements together via nesting.
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It’s very
likely you’ll have a condition you evaluate that won’t be the last nuance of
the question. For example, you might ask what team someone is in but then need
to know what business area they are assigned to. They could be in the testing
team, but more specifically in the UI testing team. Knowing that could make a
whole bunch of difference as to who knows… what tools they have access to, the
SharePoint site they can use, etc.
Putting an
If statement inside an If statement is the easiest way. Though caveat number 1
is they look messy (hey, pretty code is important!) and worse they can start to
look confusing. Take the approach then when using nested If statements, keep
them simple and limited. As we’ll discover, Ruby and other languages have
tidier ways of doing things like Methods, Classes and even Arrays.
Let’s start
with a straight forward If statement in the style we saw previously. In this
example we use a mix of the evaluation styles we have available and a single then as a reminder from the last post.
In your code, keep it consistent!
puts "Where are you
from?"
location = gets.chomp.downcase
if location =~ /\A(london|f)\z/ then
puts "OK, a big
city..."
elsif location ==
"scotland"
puts "ach the noo!"
elsif location ==
"pen y bont" or location ==
"bridge end"
puts "A fun town, haven't been there in years"
else
puts "Aha, I thought you
came from somewhere strange..."
end
The above
locations are a bit broad, what if we wanted to respond differently given a
person’s location? Say, having Pen Y Bont as a second question after asking if
the user comes from Wales? Let’s change the above to ask about Wales first.
elsif ["Wales","wales"].include? location then
Now we’ll
put the Pen y Bont part back in, using a nested If.
elsif ["Wales","wales"].include?
location then
puts "Which part? of
Wales"
country_part =
gets.chomp.downcase
if country_part ==
"pen y bont" or country_part ==
"bridge end"
puts "A fun town, haven't been there in years"
end
In this way
we have a nested If statement that will only be called if the user comes from
Wales. If so, we have another variable called country_part to capture which
part of Wales, Bridegend in this case. Just like our ‘outer’ if, it’s an
if-code-end format and yes you could add elsif
and else in there too.
puts "Where are you from?"
location = gets.chomp.downcase
if location =~ /\A(london|f)\z/ then
puts "OK, a big
city..."
elsif ["Scotland","scotland"].include? location
puts "ach
the noo!"
elsif ["Wales","wales"].include? location then
puts "Which part? of
Wales"
country_part =
gets.chomp.downcase
if country_part == "pen y bont" or country_part == "bridge end"
puts "A
fun town, haven't been there in years"
elsif country_part =~ /\A(cardif)\z/
puts "Nice
Castle there..."
else puts "Hmm... never been
there! Ydych chi'n siarad Cymraeg?"
#watch
Google translate get that wrong...
end
else
puts "Aha, I thought you
came from somewhere strange..."
end
Not bad,
covers quite a bit and is still fairly readable. However, you’re probably
already getting a sense of how a larger nested If statement will easily become
difficult to read. Use with caution. Even with our current limited knowledge of
Ruby we could be combining Arrays for
data, with Case for control and
sprinkling some If statements for a
little decision making and it would be neater.
Bonus question: Can you spot the bug in
the above code? It won’t fail as such, it’ll just give an undesired response for an ‘odd’ input.
Spoiler: if location =~ /\A(london|f)\z/
then
The f is an alternate that
shouldn’t be there, copy and paste error! Was (flee|f), the user can type
Flee or f and it will mean the same. Woops. Can you think of a way to use this feature?
Mark.
Read More
http://cyreath.blogspot.co.uk/2014/05/ruby-w-vs-w-secrets-revealed.html
http://cyreath.blogspot.co.uk/2014/05/ruby-variables-and-overview-of-w-or-w.html
http://cyreath.blogspot.co.uk/2014/05/ruby-variables-and-overview-of-w-or-w.html
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