conditionals.md

JumpStart Live (JSL)

Day 2

Conditionals

Conditionals are a programming construct that will allow you to control the flow of a program through branching (they allow your program to make decisions)

if/elsif/else Statements

• elsif and else statements can only be used when paired with an if

# independent tests; not exclusive
# 0, 1, or many of the statement(s) may execute
# every test in every if block is checked
if test
  statement(s)
end
if test
  statement(s)
end
if test
  statement(s)
end

# 0, or 1 of the if blocks may execute
# at most only 1 of the if blocks execute
# it could be the case that 0 if blocks execute because their is no else
if test
  statement(s)
elsif test 
  statement(s)
elsif test
  statement(s)
end

# mutually exclusive
# exactly 1 of the if blocks will execute
if test
  statement(s)
elsif test
  statement(s)
else
  statement(s)
end

Postfix Conditional

A way to shorten your code, when you only have one test to perform.

name = gets.chomp
puts "You're rad!" if name == "Issa" 

drink = gets.chomp
puts "Drink more water!" unless drink == "water"

Case Statements

• A good option when you are wanting to test a number of cases on a single variable

grade = gets.chomp
case grade
when "A"
  puts "Good job"
when "B"
  puts "Okay job"
when "C"
  puts "You did a job"
when "D"
  puts "You might have to do the job again"
when "E"
  puts "You have to do the job again"
end

grade = gets.chomp
case grade
when "A", "B", "C"
  puts "You passed"
when "D"
  puts "You barely passed"
when "E"
  puts "You did not pass"
end

Practice Problems

1. Single if statement

Questions

• What is the boolean expression in the code below?
• Provide a value of test_score that will cause the code to print You got an A!
• Provide a value of test_score that will cause the code to not print anything

test_score = gets.chomp.to_i

if test_score > 90
  print "You got an A!"
end

2. if/else statement

Questions

• What is different about the examples below?
• Will they work the same, even though their code is different?

test_score = gets.chomp.to_i

if test_score != 90
  puts "You got an A!"
else
  puts "You did not get an A!"
end

test_score = gets.chomp.to_i

if test_score > 90
  puts "You got an A!"
else
  puts "You did not get an A!"
end

3. if/else statement

Questions

• What is different about the examples below?
• Will they work the same, even though their code is different?

test_score = gets.chomp.to_i

if test_score < 90
  puts "You did not get an A!"
else
  puts "You got an A!"
end

test_score = gets.chomp.to_i

if test_score > 90
  puts "You got an A!"
else
  puts "You did not get an A!"
end

4. if/elsif/else statement

Questions

• What will be output if the user enters FedEx? How about usps? What about mailing?

carrier = gets.chomp

if carrier == "UPS"
  puts "United Parcel Service"
elsif carrier == "USPS"
  puts "United States Postal Servce"
elsif carrier == "FedEx"
  puts "Federal Express"
else
  puts "Mail!"
end

Resources

• Ada Conditionals Video (14:21)