Conditionals
This chapter will explore Ruby basic control structures.
Table of contents
- What’s conditionals
- True & False definition in Ruby
- Logic operation
if&elsestatementunlessstatementcasestatement
What’s conditionals
I want to know how many years of Philippine Independence. create independent2years.rb
year_of_independent = 1898
current_year = ARGV[0].to_i
how_many_years = current_year - year_of_independent
puts how_many_years
Try this code
$~ ruby independent2years.rb 2022
124
But it has some problems. Once I want to check 1811, the return value will be negative.
$~ ruby independent2years.rb 1811
-87
We need to use conditionals, if current year earlier than year_of_independent, we need to show some messages.
True & False definition in Ruby
| True | except false and nil, other values are True |
| False | false and nil |
It has a convention, the method returns the value is true or false, the method naming ? should be the least letter.
irb(main):001:0> "".empty?
=> true
irb(main):002:0> "Koda".empty?
=> false
Logic operation
Ruby use &&(and) ||(or) in multiple conditions
condition_1 && condition_2
Both condition_1 and condition_2 are True. It will return true.
irb(main):001:0> true && true
=> true
irb(main):002:0> true && false
=> false
irb(main):003:0> false && true
=> false
irb(main):004:0> false || false
=> false
irb(main):005:0> false && 1
=> false
irb(main):006:0> true && 1
=> 1 -> if 1 is True
irb(main):007:0> 'a' && 1
=> 1 -> if 1 is True
irb(main):008:0> nil && 1
=> nil -> if nil is False
irb(main):009:0> nil || nil
=> nil
condition_1 || condition_2
One of condition_1 or condition_2 is True, it will return true.
irb(main):001:0> true || true
=> true
irb(main):002:0> true || false
=> true
irb(main):003:0> false || true
=> true
irb(main):004:0> false || false
=> false
irb(main):005:0> false || 1
=> 1 -> if 1 is True
irb(main):006:0> true || 1
=> true
irb(main):0-7:0> 'a' || 1
=> "a" -> if "a" is True
irb(main):008:0> nil || 1
=> 1 -> if 1 is True
irb(main):009:0> nil || nil
=> nil -> if nil is False
if & else statement
if is the most basic conditional
if {condition}
{code block}
end
irb(main):001:0> stop_light = 'red'
=> "red"
irb(main):002:0> if stop_light == 'red'
irb(main):003:1> puts 'You should stop'
irb(main):004:1> end
You should stop
=> nil
Ruby if modifier
irb(main):001:0> stop_light = 'red'
=> "red"
irb(main):002:1> puts 'You should stop' if stop_light == 'red'
You should stop
=> nil
multiple conditionals
if {condition 1}
{code block 1}
elsif {condition 2}
{code block 2}
elsif {condition 3}
{code block 3}
else
{code block 4}
end
irb(main):001:0> stop_light = 'yellow'
=> "yellow"
irb(main):002:0> if stop_light == 'red'
irb(main):003:1> puts 'You should stop'
irb(main):004:0> elsif stop_light == 'green'
irb(main):005:1> puts 'You can go'
irb(main):006:0> elsif stop_light == 'yellow'
irb(main):007:1> puts 'You should go carefully'
irb(main):008:0> else
irb(main):009:1> puts 'The Stop light not work'
irb(main):010:1> end
you should go carefully
=> nil
unless statement
unless is the exact opposite of if. It’s a negated if.
unless {condition}
{code block}
end
irb(main):001:0> stop_light = 'green'
=> green
irb(main):002:0> unless stop_light == 'red'
irb(main):003:1> puts 'You should go'
irb(main):004:1> end
You should go
=> nil
Ruby can put else with another code block
unless {condition}
{code block 1}
else
{code block 2}
end
irb(main):001:0> stop_light = 'red'
=> "red"
irb(main):002:0> unless stop_light == 'red'
irb(main):003:1> puts 'The should go'
irb(main):004:0> else
irb(main):005:1> puts 'You should stop'
irb(main):006:1> end
You should stop
=> nil
Ruby unless modifier
irb(main):001:0> stop_light = 'green'
irb(main):002:1> puts 'You should go' unless stop_light == 'red'
You should go
=> nil
case statement
Whenever you need to use some if / elsif statements, you could consider using a Ruby case statement instead.
case {variable}
when {value 1}
code block 1
when {value 2}
code block 2
when {value 3}
code block 3
else
code block 4
end
irb(main):001:0> stop_light = 'yellow'
=> "yellow"
irb(main):002:0> case stop_light
irb(main):003:0> when 'red'
irb(main):004:1> puts 'You should stop'
irb(main):005:0> when 'green'
irb(main):006:1> puts 'You can go'
irb(main):007:0> when 'yellow'
irb(main):008:1> puts 'You should go carefully'
irb(main):009:0> else
irb(main):010:1> puts 'The Stop light not work'
irb(main):011:1> end
you should go carefully
=> nil
another example, create file case_class.rb
# case_class.rb
array = ["a", 1, nil]
array.each do |variable|
case variable
when String
puts "#{variable} is a String"
when Numeric
puts "#{variable} is a Numeric"
else
puts "#{variable} is something"
end
end
run ruby case_class.rb
$~ ruby case_class.rb
a is a String
1 is a Numeric
is something