advanced_loops.md

JumpStart Live (JSL)

Day 4

Advanced Loops

Fencepost Problems

• Sometimes illustrated as |-|-|-|-| with the | representing a fence post and the - representing the wire of the fence
• The idea is that you need 1 more post than you do wire sections; you begin with a post and end with a post
• Also sometimes called a loop-and-a-half
• Common solutions usually have the loop run one less times than needed and then handle the last post outside of the loop

Examples

# handles the first post outside the loop
# prints a comma separated list of numbers from 1 up to max
print "Max: "
max = gets.chomp.to_i
print 1
(2..max).each do |num|
	print ", #{num}" 
end

# handles the last post outside the loop
# prints a comma separated list of numbers from 1 up to max
print "Max: "
max = gets.chomp.to_i
(1..max - 1).each do |num|
	print "#{num}, " 
end
print max

Loops with logical operators

print "Please enter a number greater than 0 and less than 100: "
num = gets.chomp.to_i

while num < 1 || num > 99
	puts "Please follow the directions!"
	print "Please enter a number greater than 0 and less than 100: "
	num = gets.chomp.to_i
end

puts "You entered #{num}"

print "Please enter a number greater than 0 and less than 100: "
num = gets.chomp.to_i

until num > 0 && num < 100
	puts "Please follow the directions!"
	print "Please enter a number greater than 0 and less than 100: "
	num = gets.chomp.to_i
end

puts "You entered #{num}"

Resources

• Ada Advanced Loops Video (5:02)