Conditionals & Loops

day_2_morning.rb

#FLOW CONTROL
- Conditionals;
- Loops;

#PATH
- echo $PATH - shows all the paths the computer searches through (the paths are separated by a colon);  
- which - will tell you which programme was run (if two files have the same name, it will run the first one found in the path); 
- The ruby language will allow you to get hold of the process.id
- If you type irb into terminal, you can then type Process.pid to get the process id; 

#CONDITIONALS
- 3 < 5 => true
- 3 <= 5 => true
- 3 > 5 => false
- 5 == 5 => true
- 5 != 5 => false
- !true => false
- !false => true
- ! (5 > 3) => false

#IF ELSE STATMENTS
if 5 < 7
  puts "5 is less than 7"
elsif 5 < 3
  puts "5 is less than 3"
else
  puts "I dont know!"
end

score = 75
if score >= 80
  puts "A grade"
elsif score >= 70
  puts "B grade"
else
  puts "F"
end

=> "B grade"

- We are comparing score 3 times throughout the if else statement, this is not very DRY, use a CASE statment instead;

#CASE STATEMENT
brother = "Graucho"
case brother
when "Graucho"
  puts "cigar"
when "Harpo"
  puts "Piano"
when "Chico"
  puts "piano"
end

#LOOP
- While statement will continue to execute code while statement is true;

#WHILE LOOP1
while true
  'puts this is also true'
end

- The while loop above is an infinite loop - AVOID THIS!

#WHILE LOOP2
i = 0
while i < 25
  print "#{i} is less than 25"
  i = i + 1
end

#WHILE LOOP3
puts "Please enter a number"
i = gets.chomp.to_i
puts "You entered #{i}, thank you!"
while i < 25
  print "#{i} is less than 25"
  i = i + 1
end

#WHILE LOOP4
puts "What is 2 to the 16th power"
answer = gets.chomp.to_i
while (2**16) != answer
    puts "Wrong"
    answer = gets.chomp.to_i
end


-Chomp takes off the new line character;

puts "What is your first name?"
first = gets.chomp
puts "You typed #{first}"
puts "What is your last name"
last = gets.chomp
puts "Your last name is #{last}"

#IF STATEMENTS REVERSE ORDER; 
puts "you are old" if age < 50

#FUNCTIONS
- Functions are first class; 

def area(length, width)
    a = length * width
    a
end

def volume(length, width, height)
    area(length, width) * height
end

#You can call a function within a function

def square(x)
    x * x
end

def cube(x)
    x * x * x
end

puts volume(square(5), cube(9), 77)

def name_tag_generator(first, last, gender, age)
    if gender == 'f'
        if age < 19
            puts "Miss #{first} #{last}"
        else
            puts "Ms #{first} #{last}"
        end
    else
        puts "Mr #{first} #{last}"
    end
end

#RESOURCE
- [RUBY](http://http://ruby-doc.org/)

#COMMAND LINE SHORTCUTS
- Reverse search in command line: ctrl + r and then start typing the file name and it will complete it; 
- Press the up key to get previous commands; 
- Ctrl + c (to kill a programme in the terminal); 
- cmd + / (to comment out code);
- Ctrl + l to clear the screen;