The most common control structure, in any programming language, is
the conditional. This is a way
of telling the computer to conditionally execute some code: to execute
it only if some condition is satisfied. The condition is an
expression—if it evaluates to any value other than
nil, then the condition is satisfied.
Ruby has a rich vocabulary for expressing conditionals. The syntax choices are described in the subsections that follow. When writing Ruby code, you can choose the one that seems most elegant for the task at hand.
The most straightforward of the conditionals is
if. In its simplest form, it looks like
end is executed if (and only if) the
expression evaluates to something other
must be separated from the
a newline or semicolon or the keyword
then. Here are two ways to write the same simple
# If x is less than 10, increment it if x < 10 # newline separator x += 1 end if x < 10 then x += 1 end # then separator
You can also use
then as the
separator token, and follow it with a newline. Doing so makes your
code robust; it will work even if the newline is subsequently
if x < 10 then x += 1 end
Programmers who are used to C, or languages whose syntax is
derived from C, should note two important things about Ruby’s
Parentheses are not required (and typically not used) around the conditional expression. The newline, semicolon, ...