CS 3723 Loops and Iterators

Notes on Simple Loops and Iterators Suppose cond is some condition and code is a batch of code.
Bold words are keywords, and "each" is a method.

while cond [do] code end

code while cond

begin code end while cond

until cond [do] code end

code until cond

begin code end until cond

while cond [do] code end	code while cond	begin code end while cond
until cond [do] code end	code until cond	begin code end until cond

for i in 0..5 do code end

(0..5).each do |i| code end

(0..5).each {|i| code } # { } with single-line iterators

for i in 0..5 do code end	(0..5).each do \|i\| code end	(0..5).each {\|i\| code } # { } with single-line iterators

In the last three loops, the two on the right are exactly the same,
and they define a scope for local variables, while the one on the left does not.
The vertical bars | i | define the loop variable.
This center and right ones are Ruby iterators.

A break terminates a loop.

Iterators from Methods on the Integer Class


5.downto(1) {|n| prints n, ".. " }
   prints: 5.. 4.. 3. 2.. 1..

5.times do |i|
  print i, " "
end
   prints: 0 1 2 3 4

do end  and { } are the same
   Convention: Use { } on one line, do end multi-line

5.upto(10) {|i| print i, " " }

Iterators from Range Objects

(start .. end) and (start ... end) create Range objects
Along with each, these create an iterator:

(10..15).each do |n|
  print n, ' '
end
   prints: 10 11 12 13 14 15

for i in 1..3
  print i, " "
end
   prints: 1 2 3

for i in 1...3
  print i, " "
end
   prints: 1 2

Iterators from arrays

[1, 3, 5, 7].each {|i| print i, " " }
   prints: 1 3 5 7


for i in [1, 3, 5, 7]
  print i, " " }
end
   prints: 1 3 5 7