Home » Ruby programming

Ruby nested for loop with examples

Nested for loop in Ruby: In this tutorial, we are going to learn about the nested for loop in Ruby programming language with syntax and examples.
Submitted by Hrithik Chandra Prasad, on August 01, 2019

Nested for loop

Nesting of for loop means one for loop is available inside another for loop. It means that there are two loops, then the first one is an outer loop and the second one is the inner loop. Execution will take place in the manner that first the outer for loop is triggered, then if the condition is matched the pointer will be passed to the inner loop. Here also if the condition is satisfied, the inner for loop body will be executed until specified condition does not comes out to be false. Once the inner loop completes its execution, the pointer will be passed back to the outer for loop for its successful execution.

In Ruby, Nesting of for loop can be done with the help of the following syntax:

    for variable_name[, variable...] in expression [do]
        #expressions
        for variable_name[, variable...] in expression [do]
            # code to be executed
        end
        #expressions
    end

Example 1:

=begin 
Ruby program to demonstrate nested for loop
=end

puts "Enter upper limit"
ul=gets.chomp.to_i
puts "Enter Lower limit"
ll=gets.chomp.to_i

for i in ll..ul do
     for i in 0..3 do
     		puts "Inner loop triggered"
     	end
     	puts "Outer loop triggered"
end

Output

Enter upper limit
90
Enter Lower limit
85
Inner loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Outer loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Outer loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Outer loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Outer loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Outer loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Inner loop triggered
Outer loop triggered

You can observe in the above example that first the outer for loop is invoked then the pointer has moved to inner loop and it is printing the message for times.

Once the inner for loop completes its task, the pointer goes back to the outer loop.

Example 2:

Patterns can also be printed using nested for loop. Now let us have a quick view of how the following pattern can be printed.

*
**
***
****
*****

Code:

=begin 
Ruby program to print a pattern using nested for loop
=end

for i in 1..5 do
     for j in 1..i do
     		print "*"
     	end
     	puts ""
end