Grammar #

whileconditional[do]codeend

Or

Grammar #

whileconditional[:]codeend

When conditional is true, execute code .

In grammar do or : can be omitted without writing. But if you want to write it in one line `` While`` type, you must use the do or : separate conditional or program blocks.

Example #

#!/usr/bin/ruby#-*- coding: UTF-8
-*-$i=0$num=5while$i<$numdoputs("In a loop statement i = #$i")$i+=1end

The output result of the above example is:

In a loop statement, i=0
In a loop statement, i=1
In a loop statement, i=2
In a loop statement, i=3
In a loop statement, i=4

Grammar #

codewhilecondition or begincodeendwhileconditional

When conditional is true, execute code .

If while modifier follows a no rescue or ensure of the clause begin after the statement code will be in conditional execute once before judgment.

Example #

#!/usr/bin/ruby#-*- coding: UTF-8 -*-$i=0$num=5beginputs("In a loop statement i
= #$i")$i+=1endwhile$i<$num

The output result of the above example is:

In a loop statement, i=0
In a loop statement, i=1
In a loop statement, i=2
In a loop statement, i=3
In a loop statement, i=4

Grammar #

untilconditional[do]codeend

When conditional is false, execute code .

In grammar do can omit it. But if you want to write a until type, you must use the do separate conditional or program blocks.

Example #

#!/usr/bin/ruby#-*- coding: UTF-8
-*-$i=0$num=5until$i>$numdoputs("In a loop statement i = #$i")$i+=1;end

The output result of the above example is:

In a loop statement, i=0
In a loop statement, i=1
In a loop statement, i=2
In a loop statement, i=3
In a loop statement, i=4
In a loop statement, i=5

Grammar #

codeuntilconditional or begincodeenduntilconditional

When conditional is false, execute code .

If until modifier follows a no rescue or ensure of the clause begin after the statement code will be in conditional execute once before judgment.

Example #

#!/usr/bin/ruby#-*- coding: UTF-8 -*-$i=0$num=5beginputs("In a loop statement i
= #$i")$i+=1;enduntil$i>$num

The output result of the above example is:

In a loop statement, i=0
In a loop statement, i=1
In a loop statement, i=2
In a loop statement, i=3
In a loop statement, i=4
In a loop statement, i=5

Grammar #

forvariable[,variable...]inexpression[do]codeend

First evaluate the expression to get an object, and then target the expression execute each element in the code .

Example #

#!/usr/bin/ruby#-*- coding: UTF-8 -*-foriin0..5puts"The value of a local variable is
#{i}"end

Here, we have defined the range 0. 5. The statement for i in 0.. 5 allows the value of I from 0 to 5 (inclusive).

The output result of the above example is:

The value of the local variable is 0
The value of the local variable is 1
The value of the local variable is 2
The value of the local variable is 3
The value of the local variable is 4
The value of the local variable is 5

for...in loop is almost exactly equivalent to:

(expression).eachdo\|variable[,variable...]\|codeend

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

In grammar do can omit it. But if you want to write a for type, you must use the do separate conditional or program blocks.

Example #

#!/usr/bin/ruby#-*- coding: UTF-8
-*-(0..5).eachdo\|i\|puts"The value of a local variable is #{i}"end

The output result of the above example is:

The value of the local variable is 0
The value of the local variable is 1
The value of the local variable is 2
The value of the local variable is 3
The value of the local variable is 4
The value of the local variable is 5

Grammar #

break

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

Example #

#!/usr/bin/ruby#-*- coding: UTF-8
-*-foriin0..5ifi>2thenbreakendputs"The value of a local variable is #{i}"end

The output result of the above example is:

The value of the local variable is 0
The value of the local variable is 1
The value of the local variable is 2

Grammar #

next

Skip to the next iteration of the loop. If called within a block, the execution of the block is terminated yield expression returns nil ).

Example #

#!/usr/bin/ruby#-*- coding: UTF-8
-*-foriin0..5ifi<2thennextendputs"The value of a local variable is #{i}"end

The output result of the above example is:

The value of the local variable is 2
The value of the local variable is 3
The value of the local variable is 4
The value of the local variable is 5

Grammar #

redo

Restart the iteration of the innermost loop without checking the loop conditions. If called within a block, start over yield or call .

Example #

#!/usr/bin/ruby#-*- coding: UTF-8
-*-foriin0..5ifi<2thenputs"The value of a local variable is #{i}"redoendend

This will produce the following results and enter an infinite loop:

The value of the local variable is 0
The value of the local variable is 0
............................

Grammar #

retry

If retry appear in begin of the expression rescue clause, then from the begin the beginning of the subject starts over.

begindo_something#Exception thrownrescue
#process errorretry#Starting from begin againend

If retry appears within an iteration, within a block, or for within the body of the expression, the iterative call is restarted. The parameters of the iteration are reevaluated.

foriin1..5retryifsome_condition#Starting from i==1 again end

Example #

#!/usr/bin/ruby#-*- coding: UTF-8
-*-foriin1..5retryifi>2puts"The value of a local variable is #{i}"end

This will produce the following results and enter an infinite loop:

 The value of the local variable is 1
 The value of the local variable is 2
 The value of the local variable is 1
 The value of the local variable is 2
 The value of the local variable is 1
 The value of the local variable is 2
............................