variable?

First of all, variables are often compared to something like a box for storing values such as strings. A simple example is given below.


a = "tanaka"
b = 20
puts a  #The output of the terminal is "tanaka"
puts b  #The output of the terminal is "20"

The variable "a" is on the left side of the above "=", and the value "tanaka" is on the right side. The value "tanaka" is assigned to the variable "a". The numerical value "20" is assigned to the variable "b" below it.

Ruby uses "" "(double quotation marks) when entering a string. And since "" "" is not necessary when entering a numerical value, "" "" is removed when entering a numerical value. And below that, I use the puts method to call "a" and "b" to display the values "tanaka" and "20" inside. The operator "=" used here is called the assignment operator.

Notes on using Ruby variables

There are some caveats when using variables.

Do not use reserved words, cannot use
Define variables so that they always start with lowercase letters or "_" (underscore), not numbers! (Snake case)

1. Do not use reserved words, cannot use

In the first place, talk about reservations ...?

To put it simply, reserved words are things that cannot be used for variables, constants, etc., things that the word has a role to play.

For example, "if" for bifurcation processing is a reserved word. "Class" for defining a class is also a reserved word. Using these will return an error.

Be aware of this reserved word when defining variables!

List of reserved words


BEGIN    class    ensure   nil      self     when
END      def      false    not      super    while
alias    defined? for      or       then     yield
and      do       if       redo     true     __LINE__
begin    else     in       rescue   undef    __FILE__
break    elsif    module   retry    unless   __ENCODING__
case     end      next     return   until

Reference articles for reserved words https://docs.ruby-lang.org/ja/latest/doc/spec=2flexical.html

2. Define variables so that they always start with lowercase letters or "_" (underscore), not numbers! (Snake case)

It's important to define variables! !! !! !! !!

20 = 20 #It starts with a number, so an error occurs! !! !! !!

_20 = 20 #It starts with an underscore, so it can be defined as a "variable"! !! !! !!

number = 20 #Since it is lowercase, it can be defined as a "variable"! !! !! !! !! !!

Number = 20 #Since it is a capital letter, it is regarded as a "constant"! !! !! !! !! !! !!

Note that variables have naming conventions like this!

What is a snake case ...?

A snake case is to start a word with a lowercase letter and connect the connecting parts with "_" (underscore).

There are other "camel cases" and "upper camel cases", but they are not relevant to this article and will be omitted. If you are interested, please check it out.

Hmm? Doyukoto ...?

Here are some examples.

user_name = "tanaka"
user_age = 20

puts user_name  #The output of the terminal is "tanaka"
puts user_age #The output of the terminal is "20"

It is called snake case to put "_" between "user" and "name" which are "user_name". The same is true for "user_age".

Snake case reference article https://wa3.i-3-i.info/word1180.html

Note that in Ruby, if the beginning is capitalized when defining a variable, it will be regarded as a constant. If you are concerned about the constant, please check it.

Summary

-Variables are like boxes for storing values, and variables are defined using the assignment operator "=". ・ Notes on variable definition, do not start with numbers! Start with lowercase letters or _ (underscore)! ・ Add _ (underscore) to connect lowercase letters!

Reference article https://docs.ruby-lang.org/ja/latest/doc/spec=2fvariables.html

About Ruby variables