Conditional Statements

Conditionals are used to add branching logic to your programs; they allow you to include complex behaviour that only occurs under specific conditions.

Here is the syntax of an if statement:

if condition
  something to be done
end

condition is an expression that can be checked for truth. If the expression evaluates to true, then the code within the block is executed.

Here are some examples of expressions that evaluate to true:

3 < 4
true
"cat" == "cat"

You can combine if with the keyword else. This lets you execute one block of code if the condition is true, and a different block if it is false.

if condition
  something to be done
else
  something to be done if the condition evaluates to false
end

The else block will only be executed if the if block doesn't run, so they will never both be executed.

When you want more than two options, you can use elsif. This allows you to add more conditions to be checked.

Here is if/elsif/else statement syntax:

if condition
  something to be done
elsif different condition
  something else to be done
else
  another different thing to be done
end

Still only one of the code blocks will be run, because the statement only executes the code in the first applicable block; Once a condition has been satisfied, the whole statement ends.

Below is an actual example of an if statement with both an elsif and an else.

booleanOne = true
randomCode = "Hi!"
if booleanOne
  puts "I will be printed!"
elsif randomCode.length>=1
  puts "Even though the above code is true, I won't be executed because the earlier if statement was true!"
else
  puts "I won't be printed because the if statement was executed!"
end

Exercise

Change the value of language so that the elsif statement is the only block being executed.