Introduction to Ruby Loops - Using While, Until, For, Break, Next , Redo, Retry

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Introduction to Ruby Loops - Using While, Until, For, Break, Next , Redo, Retry

**Ruby while statement**

This typically looks something like this :

while condition

code to execute

end

For instance, suppose we need to display 1 to 5 using while.

i = 0

while i < 5

i += 1

puts i

end

This will display

Or, we can even try it out quickly in the Interactive Ruby Shell (irb) :

irb(main):026:0> i = 0

=> 0

irb(main):027:0> while i < 5

irb(main):028:1> i += 1

irb(main):029:1> puts i

irb(main):030:1> end

1

2

3

4

5

=> nil

Begin-End-While

Another way to use "while" is the begin-end-while group of statements.

begin

[instructions]

end while [some condition is true]

For example, the following code, will display 1 to 6 on a new line.

begin

i = i + 1

puts i

end while i < 6

Output

Let's try this out in irb and here's what it looks like :

irb(main):046:0> i = 0
=> 0
irb(main):047:0> begin
irb(main):048:1* i = i + 1
irb(main):049:1> puts i
irb(main):050:1> end while i < 6
1
2
3
4
5
6
=> nil

In general, 'while' executes code when the conditional is true.

There is an "until" keyword, which indicates that the corresponding code block will be executed till the condition is false.

Until modifier in Ruby

i = 0

begin

i = i + 1

puts i

end until i > 6

This displays :

When i = 7, the condition (i >6) becomes true and so the loop terminates.

**Ruby for Statement**

To give you an idea of what a Ruby for loop looks like, here's a loop which displays 1 to 5

for counter in 1..5

puts counter

end

The output ( 1 to 5 on new lines) :

A neater equivalent to the for loop (more on the lines of the foreach idea) :

(1..5).each{ |num|

puts num

end

The output ( 1 to 5 on new lines) :

**Ruby break Statement**

This terminates the innermost loop.

i = 1

while i > 0

puts i

break if i == 2

i += 1

end

Output :

(and the loop breaks immediately after that)

**Ruby next Statement**

This jumps to the next immediate iteration of the innermost loop.

For example, the following loop will keep skipping to the next loop, and only proceeds beyond the next statement when i becomes 3.

for j in 0..4

if j<2

next

end

puts j

end

Output:

( When j = 0 and j = 1, the loop skips to the next iteration as soon as it encounters the next statement. )

**Ruby redo Statement**

Restarts the iteration of the most internal loop without checking the condition

restarted = false

for x in 1..5

if x == 1

if restarted == false

puts "Re-doing when x = " + x.to_s

restarted = true

redo

end

puts x

end

Trying it out in IRB ( Interactive Ruby Shell), this is what the output looks like :

irb(main):089:0> restarted = false
=> false
irb(main):090:0> for x in 1..5
irb(main):091:1> if x == 1
irb(main):092:2> if restarted == false
irb(main):093:3> puts "Re-doing when x = " + x.to_s
irb(main):094:3> restarted = true
irb(main):095:3> redo
irb(main):096:3> end
irb(main):097:2> end
irb(main):098:1> puts x
irb(main):099:1> end
Re-doing when x = 1
1
2
3
4
5
=> 1..5

**Ruby retry Statement**

If an exception gets thrown, or if something goes wrong, this either restarts the loop (if it inside a for-loop or iteration) and if it happens to be in a begin-rescue-end expression it restarts from "begin"

The two forms look something like this :

begin

# Try to do something

rescue

retry -> An exception was thrown, start from the begin statement all over again

end

for x in 0..3

retry if something_happened

end

Check out some of our other Ruby Tutorials :

Introduction to Ruby

Introduction to Ruby and some playing around with the Interactive Ruby Shell (irb) Introduction to Ruby - Conditional statements and Modifiers: If-then, Unless, Case Introduction to Ruby Comments - Single and Multi-Line comments Introduction to Ruby Loops - Using While, Until, For, Break, Next , Redo, Retry
Introduction to Ruby - Arrays - Sorting, Filtering (Select), Transforming, Multi-Dimensional Arrays Introduction to Ruby - Strings Introduction to Ruby - Making a Script Executable Introduction to Ruby - Regular Expressions, Match, Scan
Introduction to Ruby - Computing Factorials Recursively : An Example of Recursion Introduction to Ruby - Binomial Coefficients (nCr) : An Example of Recursion Introduction to Ruby - Computing a Power Set : An Example of Recursion Introduction to Ruby - Towers of Hanoi : An Example of Recursion
Introduction to Ruby - Strings: Substitution, Encoding, Built-In Methods

Basic Data Structures With Ruby

Basic Data Structures in Ruby - Insertion Sort Basic Data Structures in Ruby - Selection Sort Basic Data Structures in Ruby - Merge Sort Basic Data Structures in Ruby - Quick Sort Functional Programming with Ruby
Basic Data Structures in Ruby - Stack Basic Data Structures in Ruby - The Queue Basic Data Structures in Ruby - Linked List - ( A Simple, Singly Linked List) Basic Data Structures in Ruby - Binary Search Tree