loops.md

Jumpstart Live (JSL)

Day 3

Loops

Definitions

Loop

Repeating a sequence of statements; telling the program to do something a certain number of times, or until a certain condition is met

Infinite loop

A loop that runs until you kill the program

Sentinel-controlled loop

When the number of loops cannot be determined prior to loop execution (e.g, while, until)

Counter-controlled loop

When the number of loops can be determined prior to loop execution (e.g, times)

Sentinel-controlled Loops

while loop

• Executes code over and over again, while a condition is true

# code syntax
while <boolean expression> do
   code
end

# code example
rand_num = rand(5)
guess = gets.chomp.to_i
while rand_num != guess do
	guess = gets.chomp.to_i
end

until loop

• Executes code over and over again, until the condition is true

# code syntax
until <boolean expression> do
   code
end

# code example
rand_num = rand(5)
guess = gets.chomp.to_i
until rand_num == guess do
	guess = gets.chomp.to_i
end

Counter-controlled Loops

times

• when times is used without an iteration variable it is a loop, when it is used with an iteration variable it becomes an iterator
• times must be associated with a block

# times syntax as a loop with no iteration variable
Fixnum.times
   code
end

# code example
# prints out "hello" 5 times
5.times do
	puts "hello"
end

Loop Table

Create a loop table for the code below, assuming the inputs noted below

puts "Hello! We are going to total some numbers!"
puts "Enter a negative number to quit."

total = 0
input = gets.chomp.to_i
while input > -1
  total += input
  input = gets.chomp.to_i
end

puts "Result: #{total}"

1. inputs; 0, -1, 2
2. inputs: 33, 6, 2, 9, 0, -1
3. inputs: 4.2, 1.1, 9.9, -1.0

Resources

• Ada Loops Video (9:11)