Conditionals in Ruby

Author: thanhluanuit

01_getting_started.md

@@ -3,6 +3,7 @@
 - Ruby is dynamic, elegant syntax, simple and productivity.
 - Creator is Yukihiro “Matz” Matsumoto.
 - Philosophy for the design of Ruby:
+
     > Ruby is designed to make programmers happy.
 
 ## Installation

02_variables.md

@@ -1,6 +1,6 @@
 # Variables
 
-## Example:
+## Examples:
 ```ruby
 welcome = 'Welcome to Ruby Programming'
 one = 1

05_conditionals.md

@@ -0,0 +1,137 @@
+# Conditionals
+
+## if
+
+```ruby
+if expression 
+  code
+end
+```
+The code between *if* and *end* is executed when the *expression* evaluates to true.
+
+Examples:
+```ruby
+# If x is greater than 5, increment x
+x = 6 
+if x > 5
+  x += 1
+end
+x #=> 7
+
+
+if 10 > 5
+  puts "10 is greater than 5"
+end
+```
+
+## else
+An *if* statement can include an **else** clause to specify code to be executed if the condition is not true:
+
+```ruby
+if expression 
+  code
+else
+  code
+end
+```
+
+Examples:
+
+```ruby
+a = 10
+b = 5
+
+if a > b
+  puts "#{a} is greater than #{b}"
+else
+  puts "#{b} is greater than #{a}"
+end
+```
+
+## elsif
+elsif is a shortened form of "else if"
+
+```ruby
+if expression_1
+  code
+elsif expression_2
+  code
+  .
+  .
+elsif expression_n
+  code
+else
+  code
+end
+```
+
+Examples:
+```ruby
+if month < 6
+  price *= 0.8  # sale of 20%
+elsif month == 6
+  price *= 0.7  # sale of 30%
+else # months in 7..12
+  price *= 0.9  # sale of 10%
+end
+```
+
+## unless
+
+```ruby
+unless expression 
+  code
+end
+```
+Same with:
+```ruby
+if !expression
+  code  
+end
+```
+- *unless* is the opposite of *if*. 
+- *unless* executes code when expression evaluates to *false* or *nil*. 
+
+Examples:
+```ruby
+x = 3
+unless x > 5   # That mean when x not greater than 5
+  x += 1       # Increment x
+end
+```
+
+
+## case
+*case* expression is an alternative to the if-elsif-else expression.
+
+Examples:
+
+```ruby
+score = 9
+
+case score
+when 1..4
+  puts "Failed!"
+when 5
+  puts "Pass!"
+when 6..7
+  puts "Not bad!"
+when 8..10
+  puts "Excellent!"
+else
+  puts "Invalid score."
+end
+```
+
+```ruby
+date = 5
+
+case date
+when 2,4,6
+  puts "Working in the morning" 
+when 3,5,7
+  puts "Working in the afternoon"
+else
+  puts "Off" 
+end
+```