Trials & Tribulations

Name Begins With	Variable Scope

$ 			A global variable 

@ 			An instance variable 

[a-z] or _	 	A local variable 

[A-Z] 			A constant

@@			A class variable

Operator	Description

+	Addition - Adds values on either side of the operator 

-	Subtraction - Subtracts right hand operand from left hand operand 

*	Multiplication - Multiplies values on either side of the operator 

/	Division - Divides left hand operand by right hand operand

%	Modulus - Divides left hand operand by right hand operand and returns remainder

**	Exponent - Performs exponential (power) calculation on operators

a, b = b, c	#Parallel assignment is also useful for swapping the values held in two variables

~	Bitwise NOT (Complement)

|	Bitwise OR

&	Bitwise AND

^	Bitwise Exclusive OR

<<	Bitwise Shift Left

>>	Bitwise Shift Right

blah = [ "b", "l", "a", "h"] #define an array

blah[2]	#access an individual element 'a'

blah[1,2]	#starting index, number of elements

blah[0..2]	#range

blah << "!"	#elements can be appended using <<

myList.uniq	#no duplicate elements

myList.uniq!	#remove duplicate elements from the array

myStack.push "blarg"	#arrays can be used like stacks (last in, first out)

myStack.pop	#pop the last element off the stack

colors.insert( 1, "orange" )	#insert new elements at the given index

colors.delete_at(1)	#delete the element at the given index

colors.delete("red")	#delete a particular element

numbers.sort	#returns a sorted array

numbers.sort!	#sorts the array

numbers.reverse	#returns a descending sorted array

Operator	Description

+		Concatinate two arrays

-		Difference - Returns a new array that is a copy of the first array with any items that also appear in second array removed.

&		Intersection - Creates a new array from two existing arrays containing only elements that are common to both arrays. Duplicates are removed.

|		Union - Concatenates two arrays. Duplicates are removed.

==		true if two arrays contain the same number of elements and the same contents for each corresponding element.

eql?		same as == except that the values in corresponding elements are of the same value type.

<=>		compares two arrays and returns 0 if the arrays are equal, -1 one if the elements are less than those in the other array, and 1 if they are greater.

Hash["a", 100, "b", 200] 

=> {"a"=>100, "b"=>200}

   h = Hash.new("Go Fish")

   h["a"] = 100

   h["b"] = 200

   h["a"]           #=> 100

   h["c"]           #=> "Go Fish"

   # The following alters the single default object

   h["c"].upcase!   #=> "GO FISH"

   h["d"]           #=> "GO FISH"

   h.keys           #=> ["a", "b"]

def methodname(param1, param2)

	...code...

end

#variable number of arguments

def displaystrings( *args )

	...code...

end



#default argument

def blah(var = "Hello World")

	...code...

end



#returns a value

def multiply(val1, val2 )

     result = val1 * val2

     return result

end

module Kenton



  # variables

  h = "Hello "

  w = "World!"

  

  def helloworld

      puts h + w

  end

end

class BankAccount

   #public instance variables

   attr_accessor :bankName 

   attr_accessor :bankNumber



   #a class variable and its accessor (shared across all instances of this class)

   def interest_rate

        @@interest_rate = 0.2

   end

   

   #an instance variable and its accessor

   def accountNumber

        @accountNumber

   end

   

   #assignment method (for assigning new values to our instance variable

   def accountNumber=( value )

        @accountNumber = value

   end



   def accountName

        @accountName

   end



   def accountName=( value )

        @accountName = value

   end

   

   #constructor

   def initialize(number)

        @accountNumber = number

   end

   

   #a custom method to calculate interest

   def calc_interest ( balance )

       puts balance * interest_rate

   end

end

#local variable created as a new instance of the BankAccount class

account = BankAccount.new()

#call the calc_interest method on the account variable

account.calc_interest( 1000 )

=> 700.0

#include statement in Ruby, if the BankAccount class is in a different file

require 'BankAccount'



class NewBankAccount < BankAccount



   def customerPhone

        @customerPhone

   end



   def customerPhone=( value )

        @customerPhone = value

   end



end

if expression then

  ...ruby code...

end

Comparison	Description

==	Tests for equality. Returns true or false

.eql?	Same as ==.

!=	Tests for inequality. Returns true for inequality or false for equality

<	Less than. Returns true if first operand is less than second operand. Otherwise returns false

>	Greater than. Returns true if first operand is greater than second operand. Otherwise returns false.

>=	Greater than or equal to. Returns true if first operand is greater than or equal to second operand. Otherwise returns false.

<=	Less than or equal to. Returns true if first operand is less than or equal to second operand. Otherwise returns false.

<=>	Combined comparison operator. Returns 0 if first operand equals second, 1 if first operand is greater than the second and -1 if first operand is less than the second.



&&	Logical `AND'

||	Logical `OR'

!	Logical negation



? :	Ternary if-then-else

if customerName == "Fred"

      print "Hello Fred!"

elsif customerName == "John"

      print "Hello John!" 

elsif customername == "Robert"

      print "Hello Bob!"

else 

      print "You're not Fred! Where's Fred?"

end



unless i >= 10

    puts "Student failed"

else

    puts "Student passed"

end

#Ternary

customerName == "Fred" ? "Hello Fred" : "Who are you?"

car = "Patriot"



manufacturer = case car

   when "Focus" then "Ford"

   when "Navigator" then "Lincoln"

   when "Camry" then "Toyota"

   when "Civic" then "Honda"

   when "Patriot" then "Jeep"

   when "Jetta" then "VW"

   when "Ceyene" then "Porsche"

   when "Outback" then "Subaru"

   when "520i" then "BMW"

   when "Tundra" then "Nissan"

   else "Unknown"

end

i = 0

while i < 5 do

   puts i

   i += 1

   break if i == 2

end



i = 0

until i == 5

   puts i

   i += 1

end

for j in 1..5 do

     for i in 1..5 do

         print i,  " "

         break if i == 2

     end

end