Ruby Syntax ckpt

_notes

1. Interpolated strings must be enclosed in double quotes. The Ruby interpreter will not search for interpolated values in a string if single quotes are used:
```
p 'hello #{3}'
```
 
2. '#' is used as a comment in Ruby
 
3. '_' is used for readablility in numbers

4. There's a special object in Ruby named nil. Nil is a representation of nothingness. Nil is important in programming because it helps programmers determine the validity of an operation.

5. "In Ruby, the last line of code in the method is automatically returned by the method." - **That's awesome - so simple!!!**

6. Arguments don't need to be the same type. For example, the method below takes three different types of arguments. (String, Integer, Float)

7. print vs put: both methods display the arguments passed to them as STRING, puts also inserts a carriage return at the end of the output

8. Ruby has another shortcut, which allows us to create an Array from a list of Strings: the %w( ) syntax. Using this shortcut saves us from having to type a lot of double- quote characters:
irb> available_colors = %w( red green blue black ) => ["red", "green", "blue", "black"]

9.

_Output

"simple math"
3
4
3
12
"exponents"
8
"operations run on variables"
10
15
"shorthand syntax"
10
15
"math op return bool"
false
true
false
true
"comparison operator"
false
true
"PRACTICE"
"order of operations"
49
31
"combine operations using variables"
49
"combine variables w/ comp oper"
true
false
"operations on string"
"hellohellohello"
"what if I want to add a space?"
"hello hello hello "
"wow, that's cool"
"helloworld"
"adding string to number"
"p 'hello' + 3 throws an error - that's interesting - JS will do it..."
"String Interpolation"
"hello 3"
"hello 5"
"more fun w/ $ interpolation"
"3 + 4 = 7"
"3 + 4 = 7"
"staying DRY"
"5 + 333333 = 333338"
"it better because if I cange vars num1 and/or num2, I it's already taken care of in the p statement"
"After 5 years I'll have 12833.586785035119 dollars!"

nil
"o"
nil

"Hello world"
3
4444
"var1 is 300"
"var2 is 14"
"300 + 14 = 314"
"After 12 years Bob will have 735.8417318419806 dollars!"
"After 12 years Joe will have 4983.988855879855 dollars!"

"<a href='http://google.com'>Google</a>"

_questions

1. What really is nil - why is it important - for instance, tut says: "...important because it helps programmers determine the validity of an operation."  Can you give me some examples where this is used in a program?

Ruby Syntax Checkpoint

# Math Operations

p "simple math"
p 1+2
p 5-1
p 6/2
p 4*3
p "exponents"
p 2**3
p "operations run on variables"
x=10
p x
x = x+5
p x
p "shorthand syntax"
x=10
p x
x += 5
p x
p "math op return bool"
p 4>5
p 3<6
p 5>5
p 5>=5 #should return true
p "comparison operator"
p 4==5
p 3==3
#p 3=3 # just curious what this returns...
p "PRACTICE"
p "order of operations"
p (3+4) * 7
p 3+4*7
p "combine operations using variables"
sum = 3+4
p sum * 7
p "combine variables w/ comp oper"
wins = 11
losses = 5
p wins > losses
p wins == losses
p "operations on string"
hello = "hello"
p hello * 3
p "what if I want to add a space?"
p (hello + " ")*3
p "wow, that's cool"
p hello + "world"
p "adding string to number"
p "p 'hello' + 3 throws an error - that's interesting - JS will do it..."
p "String Interpolation"
p "hello #{3}"
num = 5
p "hello #{num}"
p "more fun w/ $ interpolation"
p "3 + 4 = #{3+4}"
num1 = 3
num2 = 4
p "3 + 4 = #{num1+num2}"
p "staying DRY"
num1 = 5
num2 = 333333
p "#{num1} + #{num2} = #{num1 +num2}"
p "it better because if I cange vars num1 and/or num2, I it's already taken care of in the p statement"
# principal amount
p = 10_000

# annual rate of interest
r = 0.05

# number of years
t = 5

# number of times it is compounded
n = 12

# amount accumulated
a = p * (1 + r/n) ** (n*t)

p "After #{t} years I'll have #{a} dollars!"

# Nil

p "Bloc"[7]
p "Bloc"[2]
nilly = nil
p nilly

# Methods

def hello
  "Hello world"
end

p hello

def hello2
  a = 1
  b = 2
  a + b
end

p hello2

def add(a, b)
  a+b
end

p add(2222, 2222)

# passing variables as args
num1 = 10 *30
num2 = ((3+4) *2)
num3 = add(num1, num2)
p "First number is #{num1}"
p "Second number is #{num2}"
p "Adding the 2 numbers: #{num1} + #{num2} = #{num3}"

# p = principal amount
# r = annual rate of interest
# t = number of years
# n = number of times it is compounded

def compound_interest(name, p, r, t, n)
  a = p * (1 + r/n) ** (n*t)
  "After #{n} years #{name} will have #{a} dollars!"
end

p compound_interest("Bob", 100, 0.05, 40, 12)
p compound_interest("Joe", 250, 0.06, 50, 12)

# Practice - output a hyperlink:

def link(address, text)
  "<a href='#{address}'>#{text}</a>"
end

p link("http://google.com", "Google")