Expressions

The Ruby syntax is expression-oriented.

Everything in Ruby is treated as an expression and therefore evaluates to something.
Ex. :

Control structures for conditional execution or looping, which would be treated as statements in other languages, are treated as expressions in Ruby.

In Ruby, if, case and for structures return the value of the last expression evaluated within the structure.

Control Structures - Conditional Execution

Ruby has a rich syntax for expressing conditionals – the most basic is:

if expression
  code
end

where code is executed if and only if the conditional expression evaluates to something other than false or nil.

Else clauses can be added to specify code that should be executed if the conditional expression is not true:

if expression1
  code
elsif expression2
  code
else
  code
end

There’s a shorthand way of expressing the if conditional that treats it as an expression modifier:

code if expression

Ruby also has a ?: operator, as in C/C++.

Comparison operators: ==, !=, =∼, !∼, ===.

There is a case structure in Ruby, === is the case-equality operator.

In addition to the “standard” set of conditionals, Ruby has added some that are intended to increase the readability/understandability of code.
Example:

The following is the opposite of an if statement:

until expression
  code
end

where code is executed until the conditional expression evaluates to something other than false or nil.

You cannot attach else clauses to the until conditional.

Control Structures - Iteration

The for/in loop iterates over an enumerable collection:

for var in collection do
  body
end

Exit condition loop:

while condition do
  body
end

Exit condition loop, opposite of while:

until condition do
  body
end

In Ruby, it’s more common to use iterators