Ruby loop

Ruby Loop

Ruby while statement

Grammar

while conditional [do]
   code
end

Or

<pre>
while conditional [:]
   code
end

When the conditional is true, code is executed.

Do or : in the syntax can be omitted from writing. However, to write the while equation within a row, you must separate conditional or program chunks with do or : .

Instance

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

$i = 0
$num = 5

while $i < $num  do
   puts("在循环语句中 i = #$i" )
   $i +=1
end

The output of the above examples is:

Inside the loop i = 0
Inside the loop i = 1
Inside the loop i = 2
Inside the loop i = 3
Inside the loop i = 4

Ruby while modifier

Grammar

code while condition

或者

begin 
  code 
end while conditional

When the conditional is true, code is executed.

If the while modifier follows a begin statement that does not have a rescue or security clause, code executes once before the conditional judgment.

Instance

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

$i = 0
$num = 5
begin
   puts("在循环语句中 i = #$i" )
   $i +=1
end while $i < $num

Try it out . . .

The output of the above examples is:

在循环语句中 i = 0
在循环语句中 i = 1
在循环语句中 i = 2
在循环语句中 i = 3
在循环语句中 i = 4

Ruby until statement

until conditional [do]
   code
end

When the conditional is false, code is executed.

Do in syntax can be omitted from writing. However, to write out the until equation in a row, you must separate the conditional or program chunks with do.

Instance

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

$i = 0
$num = 5

until $i > $num  do
   puts("在循环语句中 i = #$i" )
   $i +=1;
end

This results in the following:

在循环语句中 i = 0
在循环语句中 i = 1
在循环语句中 i = 2
在循环语句中 i = 3
在循环语句中 i = 4
在循环语句中 i = 5

Ruby until modifier

Grammar

code until conditional

或者

begin
   code
end until conditional

When the conditional is false, code is executed.

If the until modifier follows a begin statement that does not have a rescue or security clause, code executes once before the conditional judgment.

Instance

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

$i = 0
$num = 5
begin
   puts("在循环语句中 i = #$i" )
   $i +=1;
end until $i > $num

This results in the following:

在循环语句中 i = 0
在循环语句中 i = 1
在循环语句中 i = 2
在循环语句中 i = 3
在循环语句中 i = 4
在循环语句中 i = 5

Ruby for statement

Grammar

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

Code is executed once for each element in the expression.

Instance

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

for i in 0..5
   puts "局部变量的值为 #{i}"
end

Here, we have defined the range 0..5. The statement for i in 0..5 allows i to have values from 0 to 5 (including 5).
Try it out . . .

The output of the above examples is:

局部变量的值为 0
局部变量的值为 1
局部变量的值为 2
局部变量的值为 3
局部变量的值为 4
局部变量的值为 5

for... The in loop is almost entirely equivalent to:

(expression).each do |variable[, variable...]| code end

However, the for loop does not create a new scope for local variables.

Do in syntax can be omitted from writing. However, to write out the for equation in a row, you must separate the conditional or program chunks with do.

Instance

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

(0..5).each do |i|
   puts "局部变量的值为 #{i}"
end

The output of the above examples is:

局部变量的值为 0
局部变量的值为 1
局部变量的值为 2
局部变量的值为 3
局部变量的值为 4
局部变量的值为 5

Ruby break statement

Grammar

break

Terminates the innerst loop. If called within a block, the method of the related block is terminated (the method returns nil).

Instance

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

for i in 0..5
   if i > 2 then
      break
   end
   puts "局部变量的值为 #{i}"
end

The output of the above examples is:

局部变量的值为 0
局部变量的值为 1
局部变量的值为 2

Ruby next statement

Grammar

next

Jump to the next iteration of the inner innerst loop. If called within the block, the execution of the block (yield or call returns nil) is terminated.

Instance

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

for i in 0..5
   if i < 2 then
      next
   end
   puts "局部变量的值为 #{i}"
end

The output of the above examples is:

局部变量的值为 2
局部变量的值为 3
局部变量的值为 4
局部变量的值为 5

Ruby redo statement

Grammar

redo

Restart the iteration of the inner innerst loop without checking the loop conditions. If called within the block, start yield or call again.

Instance

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

for i in 0..5
   if i < 2 then
      puts "局部变量的值为 #{i}"
      redo
   end
end

This results in the following results and enters an infinite loop:

局部变量的值为 0
局部变量的值为 0
............................

Ruby retry statement

Grammar

retry

If retry appears in the rescue clause of the begin expression, it starts over at the beginning of the begin body.

begin
   do_something # 抛出的异常
rescue
   # 处理错误
   retry  # 重新从 begin 开始
end

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

for i in 1..5
   retry if some_condition # 重新从 i == 1 开始
end

Instance

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

for i in 1..5
   retry if  i > 2
   puts "局部变量的值为 #{i}"
end

This results in the following results and enters an infinite loop:

局部变量的值为 1
局部变量的值为 2
局部变量的值为 1
局部变量的值为 2
局部变量的值为 1
局部变量的值为 2
............................