1. Ruby
and other languages…

2. Valuable Reference
The Ruby Programming Language, Flanagan & Matsumoto (creator of Ruby)

3. Ruby Program Structure
Basic unit is expression
Primary expressions: true, false, nil, self, number and string literals, variable references (all represent values)
Expression types: arithmetic, boolean
Expressions produce a value
Statements generally do something, may contain expressions (distinction blurry sometimes)
is-the-difference-between-an-expression-and-a- statement-in-python

4. Get started option #1 - interactive
open IRB
type Ruby command, press return. Example:
puts “say Hi”
say Hi
nil
nil is return… ruby has expressions, not statements

5. Getting started option #2 – command line
Open text editor
Write ruby commands, e.g.:
puts “say Hi”
save file as demo1.rb
at command line: ruby demo1.rb
you must be in the same folder as demo1.rb
On school computers, type Z: and press return to get to the z: drive
Use cd to navigate (you’ve done this with git bash)

6. Ruby Program Structure
Code can be organized using:
Blocks
Methods
Classes
Modules

7. Program Execution Ruby is a scripting language No special main method
In general, script starts executing with line 1, continues until all lines executed
Methods/classes come into existence when they are read in the file. Method calls must be placed after the method definitions

8. Ruby Expression Structure
Whitespace: mostly ignored
Expression separators: newline
use caution if statement doesn’t fit on one line
insert newline after operator, period or comma
OR escape the newline *
* think: how does interpreter recognize tokens/statement?

9. Block Structure 10.times { puts “hello” } x = 5 unless x == 10 print x
end
Blocks can be nested. Indent for clarity.
block surrounded by { }
often call this the “body”
never delimit with { }
block delimited by “end”
Compare to Java/C++

10. Ruby Comments # This is a comment OR =begin
This is a longer comment. =begin/=end must be at the start of a line
=end

11. Variables length: no limit (afaik) valid characters:
letters, numbers, _
can’t start with number
$ used as first character of global var
used to identify instance and class variables
? (convention) end method name with ? if returns boolean
! (convention) end method name with ! if dangerous
= used to make assignments (covered with classes)
no other punctuation
support for Unicode
first letter (enforced by ruby):
Constants, classes and modules begin with A-Z
case sensitive
Compare to Java/C++/Fortran

12. Ruby Data Types: numbers
Numeric
Integer – allows base 8, 16, 2 (binary)
Fixnum: fit in 31 bits
Bignum: arbitrary size
Float – includes scientific notation
Complex
BigDecimal: use decimal rather than binary rep
Rational
C++ has unsigned ints, Java does not… concept doesn’t apply to Ruby – why?
COBOL was for business… inherent big decimal. Java/C# provide. C++ does not. Adv: accuracy. Disadv: waste space

13. A few number-related details
div = integer division, e.g., 7.div 3
fdiv = floating point division, e.g., 7.fdiv 3
quo = rational division
-7/3 = -3 in Ruby, -2 in Java/C++
Float::MAX
Infinity
Numbers are immutable (as you’d expect)

14. Ruby Data Types: strings
String literals – single quote
‘A ruby string’
‘Didn\’t you have fun?’
Only escape \’ or \\
newlines are embedded if multi-line
String literals – double quote
normal escape sequences (\t, \n etc)
string interpolation
w=5
h=4
puts "The area is #{w*h}"
Other languages with interpolation?

15. More strings Strings are mutable in Ruby
+ is concatenation (often prefer interpolation)
age = 32
puts "I am " + age.to_s
<< is append
s = "Hello"
s << " World"
puts s
Extract characters
puts s[0, 5]
* repeats text
puts "hey " * 5
Java converts right-hand to string, Ruby doesn’t

16. Characters Changed from Ruby 1.8 to Ruby 1.9
Characters are now strings of length 1
Python also has strings of length 1, not primitive chars

17. Ruby Methods No ( ) needed for function invocation Try it:
"hello".center 20
"hello".delete "lo"
note: if use (), don’t put space after fn name!
f(3+2)+1 != f (3+2)+1
What’s good practice? Here are some thoughts:

18. String Access Can use [] with, e.g., s = "cats rule"
[ix] # puts s[0]
[ix,len] # puts s[0,4]
[ix..ix] # puts s[0..3]
[-ix] #puts s[-4, 4]
puts s.length
if index too large, just returns nil
Compare to C/C++

19. String Access: Quick Exercise
Try:
s = "Sunday, Monday, Tuesday, Wednesday, Thursday, Friday"
Find different ways to extract Sunday, Monday and Friday using the index options shown above
Use different ways to modify the string (e.g., convert the string to:
Monday, day, Tuesday, Wednesday, Thursday, Saturday)
Play with RubyBasics.rb
Nothing to submit; no right answers – just play!

20. Get started
Do Ruby Intro homework

21. Topic Summary Ruby Basics Language concepts program structure
Effect of syntax on compilation
Binding
overview
static vs dynamic
explicit vs implicit types
Scripting language
Keywords vs Reserved words
Ruby Basics
program structure
program execution
block structure
methods
comments
variables
strings
interpolation
numbers

22. Extra Details May use BEGIN/END (not common to do)
BEGIN { # global init code ]
END { #global shutdown code]
if multiple BEGINS, interpreter executes in order read