If Statements

SO sometimes we have to as a question, and have a result based on that answer. For example

"I Mary doesnt have two shoes on, ask her 'why'"

For assignment is the following quesiton is given

"If Mary has more than $5, then give her an apple."

So the following code is given as an example

# define the method: Here they are defining the method that evaluates if mary can have an apple
def can_buy_apple_with?(money)
  if money > 5
    "have an apple"
  end #if statements must be closed with an end also before closing the method
end

# call the method, passing in a 7, and the method will answer with "have an apple"
can_buy_apple_with?(7)
#=> "have an apple"

# call the method, passing in a 5, and the method will answer with "nil"
can_buy_apple_with?(5)
#=> nil

Since the we need a way to answer either way, the following ELSE statement is added to the method

def can_buy_apple_with?(money)
  if money > 5
    "have an apple"
  else
    "sorry, how about some gum?"
  end 
end

We call the method two ways

# call the method, passing in a 7
can_buy_apple_with?(7)
#=> "have an apple"

# call the method, passing in a 5
can_buy_apple_with?(5)
#=> "sorry, how about some gum?"

i tried this in the editor and it worked well
the question is, what to do if the amount 5 == 5, which is where ELSEIF comes into play

So the following change in the program is suggested 

def can_buy_apple_with?(money)
  if money > 1_000
    "have an Apple computer"
  elsif money > 5
    "have an apple"
  elsif money == 5
    "have some gum"
  else
    "get out of my store"
  end
end

# call the method, passing in a 2_000
can_buy_apple_with?(2_000)
#=> "have an Apple computer"

# call the method, passing in a 6
can_buy_apple_with?(6)
#=> "have an apple"

# call the method, passing in a 5
can_buy_apple_with?(5)
#=> "have some gum"

# call the method, passing in a 4
can_buy_apple_with?(4)
#=> "get out of my store"

Note to Oliver: I spent an hour plpaying with this in IRB and got it wrong most of the time and then finally realized why we need RSPEC....Damn TYPOS!

but I digress

Unless and !

apparently Unless is used for simple logic and comparison. the example given is as follows:

def can_buy_apple_with?(money)
  unless money < 1_000
    "have an Apple computer"
  else
    "have an apple"
  end
end

Now you can refactor the code to us if statments, but to make it simpler but get the same effect, you can use !

def can_buy_apple_with?(money)
  if !(money < 1_000)
    "have an Apple computer"
  else
    "have an apple"
  end
end

basically, the ! flops the normal logic of an if statement from "if it does" to "if does not". 

One Line Conditionals

So apparently ruby lets you do small one-line conditions, such as the following;

gets_discount = true
price *= 0.8 if gets_discount

skip_tax = true
price += price * 0.1 unless skip_tax

If gets_discount is true (which it is) then you'll discount the price by 20%. Unless skip_tax is true, you'll add a 10% tag to the price.

adding statements of AND and OR, AKA && and | |

#this would read "if I have more than 5, and I am hungry, then say "give me an apple"
if money > 5 && hungry
  "give me an apple"
end

#For that method, both sides of the operator have to be true

#for this, only one side needs be true

if money > 5 || hungry
  "apple"
end

#can be refactored as

if (money > 5) || (hungry)
  "apple"
end

if statements simply look for a true or false value. To be clear, true and false values do not have to be boolean values. In Ruby, nil and false are all considered to be "false-y" values. Everything else in Ruby is naturally true. Consider the following example:

def is_true(a)
  if a
    "true"
  else
    "false"
  end
end

is_true("hello") #=> will return "true"
is_true(4)       #=> will return "true"
is_true(true)    #=> will return "true"
is_true(nil)     #=> will return "false" #fals-y value
is_true(false)   #=> will return "false" #fals-y value