Personal memo Progate Ruby I (2)

6. Variable basics

・ Variables: A box that holds values. Variables are defined by "variable name = value".

animal = "Seal"
↳ Variable name ↳ Value to be assigned

[Caution]

・ Programming "=" ⇒ It does not mean "equal".

・ Then, what is the "=" in programming? ⇒ It means "put the right value in the left variable". This flow is called "assignment".

index.rb replacement image

animal = "Seal"    　 →  animal =  "Seal" 
puts animal              →  puts "Seal" 
↳ Variable animal is the value("Seal")Replace with

>_console
Seal

[Caution]

animal="Seal"                    >_console
                
*1.puts animal seal
*2.puts "animal"                      animal

If you enclose the variable in double quotes like * 2, Since it is recognized as a character string, it is not enclosed when it is treated as a variable.

7. Let's use variables

The program is executed in order from the top

⇒ When using a variable, be sure to define the variable name.

● Variable containing a character string

-Calling a variable "replaces" the assigned value -Variables containing character strings can be handled in the same way as character strings.

message ="I"　　　　　　　　　　　
puts message + "It's a seal"　
animal = "It's an otter"

puts message + animal

>_console

I'm a seal
I'm an otter

● Variable with numerical value

　　  number1 = 20                     　　 
 puts number1 + 3                             
     number2 = 15                                  
 puts number1 + number2 

>_console

23
38

8. Roles of variables and precautions

● Why use variables? -There are many values in the program. ・ Accuracy and flexibility are required when writing programs. ⇒ One of the mechanisms to solve these two points is a variable.

● Role of variables ⇒The same element can be used repeatedly ⇒ Easy to respond to changes ⇒ Easy to understand what the elements are

・ When variables are not used

index.rb

puts "I'm a harbor seal"
puts "I'm a bearded seal"
puts "I'm a harp seal"
puts "I'm a Baikal seal"

If you replace the "I" part with "Actually I" All three must be changed.

・ When using variables

index.rb

text = "Actually I"
puts = text + "It ’s a harbor seal." 
puts = text + "It ’s a bearded seal."
puts = text + "It ’s a harp seal."
puts = text + "Baikal seal"

Substitute if you replace the "I" part with "Actually I" All you have to do is change the string.

● Easy-to-understand variable names ⇒ What value is assigned to the variable Give a variable name that can be judged

○ animal = "Seal"
×   I am = "Seal"

● Variable name rules ⇒ Ruby has some naming rules.

• Basically free.

[Caution] When assigning a variable name that combines two or more words, Use underscores (_).

Ex. Spotted_seal etc.

• The following is a bad example ・ 1seal × Starts at several hours ・ Zarashi △ Romaji ・ Seal △ Japanese

9. Variable update (1)

● Change the value of a variable

Variables can change the value once assigned. ⇒ If you assign a value to a variable that has been assigned a value once, then assign the value again. The contents are overwritten.

 index.rb　　　　　　　 >_console
 number = 1                 
 puts number             1
 number = 7
 puts number             7
⇖ The value of the overwritten variable is output.

⇒Since the program is executed in order from the top, the contents will be overwritten.

10. Variable update (2)

● Substitute for yourself

When "I want to add 3 to the value of the variable number that has already been defined" What should i do?

Answer:

                                  >_console
number = 2
puts number 　　　　　　　　　　　　　　　2

number = number + 3
puts number                            5

Add 3 to number as in the code above and assign it to number again. The number to the right of "=" is replaced with the value, and the calculated result is assigned to the number on the left.

⇒Similarly when assigning to yourself, the program is in order from the top Since it is executed, the contents are overwritten.

Application (abbreviation)

Uninflected abbreviation
x = x + 7                      x += 7
x = x -  7                     x - = 7
x = x * 7                      x * = 7
x = x / 7                      x / = 7
x = x % 7                      x % = 7

11. Variable expansion

● Variable expansion

Include variables in strings

#{Variable name} ⇒Variable expansion: How to include the value of a variable in a character string.

[Caution]

I used double quotes Variable expansion is possible only for strings. ⇒ Single quotation is NG

"" = 〇　
'' = ×

ex.In the case of otters

animal = "Otters"
puts "Hello#{name}Mr."

>_On the console

Hello otter's

● Advantages of variable expansion:

index.rb(☆)

age = 25
puts age + "I'm old"
　　 (Numerical value) (String)
---------------------
>_On the console

× Error occurred!!

--------------------------------------------------------
index.rb(★)

age = 25
puts "#{age}I'm old"

---------------------
>_On the console

25 years old

● Variable expansion

Commentary: Numerical values and character strings like ☆ It cannot be connected by addition. However, if you use variable expansion like ★ Variables with numbers can be converted to strings without any problem Can be included. ⇒ If you want to include variables in the string Basically use variable expansion.