Variables and Assignment

To store a number or a string in your computer's memory for use later in your program, you need to give the number or string a name. Programmers often refer to this process as assignment and they call the names variables. A variable springs into existence as soon as the interpreter sees an assignment to that variable.

Local variables have the quality of barewords; they must start with either a lowercase letter or the underscore character (_), and they must consist entirely of letters, numbers, and underscores. Remember, local variable references look just like method invocation expressions.

Keywords can't be used as variable names. def is a keyword; the only thing you can use it for is to start a method definition. if is also a keyword; lots of Ruby code involves conditional clauses that start with if, so it would be too confusing to also allow the use of if as a variable name.

Method calls can be barewords, such as start_here. puts is a method call; so is print. When Ruby sees a bareword, it interprets it as one of three things: a local variable, a keyword, or a method call. (a) If there's an equal sign (=) to the right of the bareword, it's a local variable undergoing an assignment. (b) If the bareword is a keyword, it's a keyword (Ruby has an internal list of these and recognizes them). (c) Otherwise, the bareword is assumed to be a method call. If no method by that name exists, Ruby raises a NameError.

The p004stringusage.rb shows us some more usage with strings.

# p004stringusage.rb
                # Defining a constant
                PI = 3.1416
                puts PI
                # Defining a local variable
                myString = 'I love my city, Pune'
                puts myString
                =begin
                  Conversions
                  .to_i, .to_f, .to_s
                =end
                var1 = 5;
                var2 = '2'
                puts var1 + var2.to_i
                # << appending to a string
                a = 'hello '
                a<<'world.
                I love this world...'
                puts a
                =begin
                  << marks the start of the string literal and
                  is followed by a delimiter of your choice.
                  The string literal then starts from the next
                  new line and finishes when the delimiter is
                  repeated again on a line on its own. This is known as
                  Here document syntax.
                =end
                a = <<END_STR
                This is the string
                And a second line
                END_STR
                puts a

In the example:
x = "100".to_i
the dot means that the message "to_i" is being sent to the string "100", or that the method to_i is being called on the string "100". The string "100" is called the receiver of the message. Thus, when you see a dot in what would otherwise be an inexplicable position, you should interpret it as a message (on the right) being sent to an object (on the left).

Summary

I have listed down all the important points you need to remember after you have completed the following topics: Introduction, Installation, First Ruby program, Features of Ruby, Numbers in Ruby, String fundamentals and Variables and Assignment.

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Variables and Assignment

Summary