Loops

Loops in Ruby are used to execute the same block of code a specified number of times. This chapter details all the loop statements supported by Ruby.

Ruby while Statement

Syntax

while conditional [do]
   code
end

Executes code while conditional is true. A while loop’s conditional is separated from code by the reserved word do, a newline, backslash \, or a semicolon ;.

Example

#!/usr/bin/ruby&dollar;i =0&dollar;num =5while&dollar;i <&dollar;num  do
   puts("Inside the loop i = #&dollar;i")&dollar;i &plus;=1end

This will produce the following result −

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

Syntax

code while condition

OR

begin 
  code 
end while conditional

Executes code while conditional is true.

If a while modifier follows a begin statement with no rescue or ensure clauses, code is executed once before conditional is evaluated.

Example

#!/usr/bin/ruby$i =0$num =5begin
   puts("Inside the loop i = #&dollar;i")&dollar;i &plus;=1endwhile&dollar;i <&dollar;num

This will produce the following result −

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 until Statement

until conditional [do]
   code
end

Executes code while conditional is false. An until statement’s conditional is separated from code by the reserved word do, a newline, or a semicolon.

Example

#!/usr/bin/ruby$i =0$num =5until$i >$num  do
   puts("Inside the loop i = #$i")$i +=1;end

This will produce the following result −

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
Inside the loop i = 5

Ruby until modifier

Syntax

code until conditional

OR

begin
   code
end until conditional

Executes code while conditional is false.

If an until modifier follows a begin statement with no rescue or ensure clauses, code is executed once before conditional is evaluated.

Example

#!/usr/bin/ruby$i =0$num =5begin
   puts("Inside the loop i = #$i")$i +=1;enduntil$i >$num

This will produce the following result −

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
Inside the loop i = 5

Ruby for Statement

Syntax

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

Executes code once for each element in expression.

Example

#!/usr/bin/rubyfor i in0..5
   puts "Value of local variable is #{i}"end

Here, we have defined the range 0..5. The statement for i in 0..5 will allow i to take values in the range from 0 to 5 (including 5). This will produce the following result −

Value of local variable is 0
Value of local variable is 1
Value of local variable is 2
Value of local variable is 3
Value of local variable is 4
Value of local variable is 5

A for…in loop is almost exactly equivalent to the following −

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

except that a for loop doesn’t create a new scope for local variables. A for loop’s expression is separated from code by the reserved word do, a newline, or a semicolon.

Example

#!/usr/bin/ruby(0..5).eachdo|i|
   puts "Value of local variable is #{i}"end

This will produce the following result −

Value of local variable is 0
Value of local variable is 1
Value of local variable is 2
Value of local variable is 3
Value of local variable is 4
Value of local variable is 5

Ruby break Statement

Syntax

break

Terminates the most internal loop. Terminates a method with an associated block if called within the block (with the method returning nil).

Example

#!/usr/bin/rubyfor i in0..5if i >2thenbreakend
   puts "Value of local variable is #{i}"end

This will produce the following result −

Value of local variable is 0
Value of local variable is 1
Value of local variable is 2

Ruby next Statement

Syntax

next

Jumps to the next iteration of the most internal loop. Terminates execution of a block if called within a block (with yield or call returning nil).

Example

#!/usr/bin/rubyfor i in0..5if i <2thennextend
   puts "Value of local variable is #{i}"end

This will produce the following result −

Value of local variable is 2
Value of local variable is 3
Value of local variable is 4
Value of local variable is 5

Ruby redo Statement

Syntax

redo

Restarts this iteration of the most internal loop, without checking loop condition. Restarts yield or call if called within a block.

Example

#!/usr/bin/rubyfor i in0..5if i <2then
  puts "Value of local variable is #{i}"redoendend</pre>


This will produce the following result and will go in an infinite loop −



Value of local variable is 0
Value of local variable is 0
............................




Ruby retry Statement



Syntax



retry




If retry appears in rescue clause of begin expression, restart from the beginning of the begin body.



begin
   do_something # exception raisedrescue# handles errorretry# restart from beginningend



If retry appears in the iterator, the block, or the body of the for expression, restarts the invocation of the iterator call. Arguments to the iterator is re-evaluated.



for i in1..5retryif some_condition # restart from i == 1end



Example



#!/usr/bin/rubyfor i in0..5retryif i >2
puts "Value of local variable is #{i}"end



This will produce the following result and will go in an infinite loop −



Value of local variable is 1
Value of local variable is 2
Value of local variable is 1
Value of local variable is 2
Value of local variable is 1
Value of local variable is 2
.................