Interesting ruby-Study notes 2

Comment Line comments are #Multi-line comments are stranger with = begin and = end

#! / usr / bin / ruby -w

puts "Hello, Ruby!"

= begin
This is a multi-line comment.
Scalable to any number of rows.
But = begin and = end can only appear on the first and last lines.
= end

Conditional judgment

if conditional [then]
	  code...
[elsif conditional [then]
	  code...]...
[else
	  code...]
end

An if expression is used for conditional execution. The value false and nil are false, and the other values are true. Note that Ruby uses elsif, not the else if and elif.
Usually we omit the reserved word then. If you want to write the complete if style in a row, then you must separate the conditional and program chunks with then. As shown below:

If a = = 4 then a = 7 end

Instance

#! / usr / bin / ruby
#-*-coding: UTF-8-*-

x = 1
if x> 2
    puts "x is greater than 2"
elsif x <= 2 and x! = 0
    puts "x is 1"
else
    puts "Unable to know the value of x"
end

Ruby Loop syntax

While conditional [do]   codeend

Or

While conditional [:]   Codeend

Do or: can omit to write in syntax. But to write down a while in a row, you must separate the conditional or program chunks with do or:.
Grammar

code while condition

or

begin
   code
end while conditional

Until is a special until grammar.

Until conditional [do]   codeend

Instance

#! / usr / bin / ruby
#-*-coding: UTF-8-*-

$ i = 0
$ num = 5

until $ i> $ num do
    puts ("i = # $ i" in a loop statement)
    $ i + = 1;
end

Forfor is generally the most used cycle mode

for variable [, variable ...] in expression [do]
   code
end

Like what

#! / usr / bin / ruby
#-*-coding: UTF-8-*-

for i in 0..5
    puts "The local variable has the value # {i}"
end

You can write it like that.

#! / usr / bin / ruby
#-*-coding: UTF-8-*-

(0..5) .each do | i |
    puts "The local variable has the value # {i}"
end

The next statement is equivalent to the Continue statement redo can start the loop again, but it is easy to cause a dead loop, and I don't know why this syntax is designed

#! / usr / bin / ruby
#-*-coding: UTF-8-*-

for i in 0..5
    if i <2 then
       puts "The local variable has the value # {i}"
       redo
    end
end

This will produce a dead loop retry statement If retry appears in the rescue clause of the BEGIN expression, start again from the beginning of the body of begin.

begin
    do_something # exception thrown
rescue
    # Handle errors
    retry # restart from begin
end

If the retry appears inside the iteration, within the block, or within the body of the for expression, the iteration call is restarted. The parameters of the iteration are re-evaluated.

for i in 1..5
    retry if some_condition # restart from i == 1
end

Instance

#! / usr / bin / ruby
#-*-coding: UTF-8-*-

for i in 1..5
    retry if i> 2
    puts "The local variable has the value # {i}"
end 

And this is another cycle of death.

Interesting ruby-Study notes 2