Loops, blocks, array & hashes.

1. RUBY BASICS - II

2. Abstract of
Session
 Loops
 Iterators & Blocks
 Array
 Hashes
 Iteration over Array and
Hashes
 Symbols
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3. Loops ?
Loops in Ruby are used to execute the same block of code a
specified number of times until some condition is met.
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4. While Loop
While loops will execute all of the statements contained within them as long as the
conditional statement remains true.
There are 3 ways to use while loop
Syntax :
1)
2)
3)
while condition do
code
end
code while condition
begin
code
end while condition
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5. Example
What is difference ?
In 2nd or 3rd case, code is executed once before conditional is evaluated.
example :
num = 0
max = 5
while num < max
puts("Inside the loop #{num}")
num += 1
end
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6. until
Executes code when condition is false.
There are 3 ways to use until loop
Syntax :
1) until condition do
code
end
2)
3)
code until condition
begin
code
end until condition
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7. For
Loop
lexample :
l
•for num in 0..5
puts("Inside the loop #{num}")
•end
lO/P :
•Inside the loop 0
•Inside the loop 1
•Inside the loop 2
•Inside the loop 3
•Inside the loop 4
•Inside the loop 5
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8. times
lexample :
l
• 5.times do |index|
puts("Inside the loop #{index}")
•end
lO/P :
•Inside the loop 0
•Inside the loop 1
•Inside the loop 2
•Inside the loop 3
•Inside the loop 4
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9. What are
iterators ?
l Another word for loop. In ruby, Iterators are nothing but methods supported by
collections.
l Objects that store a group of data members are called collections. In Ruby, arrays and
hashes can be termed collections.
l Iterators return all the elements of a collection, one after another. We will be discussing
two iterators here.
• each
• collect
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10. each
lSyntax :
•collection.each do |variable|
l
code
•end
lExample :
l
•num_array = [1,2,3,4,5]
•num_array.each do |num|
puts num
•end
lYou always associate the each iterator with a block. It returns each value of the
array, one by one, to the block. The value is stored in the variable num and then
displayed on the screen.
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11. collect
lThe collect iterator returns all the elements of a collection.
lSyntax :
•collection = collection.collect
lThe collect method need not always be associated with a block. The collect method
returns the entire collection, regardless of whether it is an array or a hash.
lexample :
•num_array = [1,2,3,4,5]
•new_array = num_array.collect{|num| 10*num}
•puts new_array
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12. What are
blocks?
lA block consists of chunks of code.
lYou assign a name to a block.
lThe code in the block is always enclosed within braces {}.
lA block is always invoked from a function with the same name as that of the block.
This means that if you have a block with the name test, then you use the function test
to invoke this block.
lYou invoke a block by using the yield statement.
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13. Blocks
lSyntax :
•block_name{
l
statement1
l
statement2
l
..........
•}
lExample :
•def test
l
puts "You are in the method"
l
yield
l
puts "You are again back to the method"
l
yield
•end
•test {puts "You are in the block"}
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14. Proc
Proc objects are blocks of code that have been bound to a set of local
variables.
Call a proc by using the variable’s call method
For Example :
p = Proc.new { |x, y, z| puts 100 * x + 10 * y + z }
p.call 14, 9, 2
=> 1492
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15. Arrays
 One array can contain any type of objects
 Grows automatically
l1) with the new class method:
nums = Array.new
nums = Array.new(10) { |e| e = e * 2 }
puts "#{nums}"
l2) There is another method of Array, [].
nums = Array.[](1, 2, 3, 4,5)
OR
nums = Array[1, 2, 3, 4,5]
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16. Hashes
lA Hash is a collection of key-value pairs like this: "employee" => "salary". It is similar to an
Array, except that indexing is done via arbitrary keys of any object type, not an integer
index.
lAs with arrays, there is a variety of ways to create hashes. You can create an empty hash
with the new class method:
lmonths = Hash.new
lExample:
•num = Hash["a" => 100, "b" => 200]
•keys = num.keys
•puts keys
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18. Questions ?

19. Thank You