Review the basic knowledge of ruby that is often forgotten

#Character string → character string
'1'.to_s   # => "1"

#Numerical value → character string
1.to_s     # => "1"

#nil → blank string
nil.to_s   # => ""

#Boolean value true → of character string"true"
true.to_s   # => "true"

#Boolean false → string"false"
false.to_s   # => "false"

#Normal writing
object.Method(Argument 1,Argument 2,Argument 3)
#You may omit the parentheses
object.Method argument 1,Argument 2,Argument 3
#With no arguments
object.Method

#Variable name should be snake case
first_name = user.first_name

#Camel case is not customarily used
firsfName = user.first_name

#Variables starting with a number will result in an error and cannot be used
2_discount_price = 200

#String
'This is a string'
"This is a string"

#When expanding an expression
i = 'String'
"this is#{i}"  # => this is文字列

# &&Is an AND logical operation
#True if both condition 1 and condition 2 are true, false otherwise
Condition 1&&Condition 2

t1 = true
t2 = true
f1 = false
t1 && t2      # => true
t1 && f1      # => false

##Condition 1 is true if either condition 2 is true, and false if both are false.
Condition 1||Condition 2

t1 = true
t2 = true
f1 = false
f2 = false
t1 || t2      # => true
t1 || f1      # => true
f1 || f2      # => false

#Returns true if it is an empty string, false if it contains characters empty?Method
''.empty?           # => true
'AIUEO'.empty?   # => false

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