Learn Ruby Programming

• Need IRB (Interactive Ruby)
  • http://rubyinstaller.org/
  • http://rubyonrails.org/download

• Simple commands

irb(main):022:0> 2 + 4
=> 6

irb(main):023:0> print "Hello World"
Hello World=> nil

irb(main):024:0> 3.times do print "Yeah" end
YeahYeahYeah=> 3

irb(main):027:0> 7/3
=> 2

irb(main):028:0> 7.0/3
=> 2.3333333333333335

• Variable

irb(main):025:0> x = 12
=> 12

irb(main):026:0> x + 13
=> 25

Variable is case-sensitive.
M = 29

M

* Shortcuts

g += 1
M *= 4

• Object Oriented - Class

irb(main):029:0> class Vehicle
irb(main):030:1> attr_accessor :name, :type, :make, :model
irb(main):031:1> end
=> nil

• Object Oriented - Instantiation - Creating an Object

irb(main):039:0> my_vehicle = Vehicle.new
=> #<Vehicle:0x29583c0>

irb(main):040:0> my_vehicle.name = "Work Car"
=> "Work Car"

irb(main):041:0> my_vehicle.make = "Honda"
=> "Honda"

irb(main):045:0> puts my_vehicle.name + " is " + my_vehicle.make
Work Car is Honda
=> nil

• Object Oriented - Inheritance

irb(main):051:0* class Bus < Vehicle
irb(main):052:1> attr_accessor :num_seats
irb(main):053:1> end
=> nil

irb(main):054:0> my_bus = Bus.new
=> #<Bus:0x282fd50>

irb(main):055:0> my_bus.make = "GMC"
=> "GMC"

irb(main):056:0> my_bus.num_seats = 30
=> 30

• Object Oriented - Method

irb(main):092:0> class Bus < Vehicle
irb(main):093:1> def show_make
irb(main):094:2> puts "Make: " + make
irb(main):095:2> end
irb(main):096:1> end
=> nil

irb(main):097:0> my_bus.show_make
Make: GMC
=> nil

• Object Oriented - What class does an object come from?

irb(main):068:0* my_bus.class
=> Bus

irb(main):069:0> 36.class
=> Fixnum

"Hello".class

• Object Oriented - Kernel Methods - No need to prefix it with Kernel.

irb(main):074:0> puts "Hello"
Hello
=> nil

irb(main):075:0> Kernel.puts "Hello"
Hello
=> nil

• Arguments

puts("hello") same as puts "hello"

* String
"Hello".length
"Hello".reverse
"Hello".upcase
"Hello".reverse.upcase  # concatenation

• Function or Method without Class

def display_hello
puts "Hello"
end

display_hello

• Conditions or decision making

puts "hello" if M < 20

• Comparison operators

==
< > <= >=
!=

• Boolean operators

&&

• Loop

8.times do puts "Hello" end

8.times {puts "Hello"}

3.upto(7) {puts "Hello"}  # 5 loops

14.downto(9) {puts "Hello"}  # 6 loops

1.step(9,2) {puts "Hello"}  # 5 loops

• Extract the loop count number

1.upto(10) {|c| puts c}

• Data type conversion

c = 13
print c.to_f/4
3.25=>nil

• Constant

> Pi = 3.14
> print Pi
3.14=> nil

> Pi = 3
warning: already initialized constant Pi

print Pi
3=> nil   # Just a warning, the value is actually changed.