Controlling the execution flow with conditionals

Crystal, like most imperative languages, has a top-to-bottom line-by-line flow of execution. After the current line is executed, the line below that will be the next one. But you are empowered to control and redirect this flow of execution based on any conditional expression you can think of. The first kind of flow control we will cover is precisely that, reacting to conditionals.

if and unless

An if statement can be used to check a conditional; if it's truthy (that is, not nil nor false), then the statement inside it is executed. You can use else to add an action in case the conditional isn't true. See this, for example:

secret_number = rand(1..5) # A random integer between 1 and 5
print "Please input your guess: "
guess = read_line.to_i
if guess == secret_number
  puts "You guessed correctly!"
else
  puts "Sorry, the number was #{secret_number}."
end

The conditional...