Ruby nested while loop with examples

By IncludeHelp Last updated : November 16, 2024

Nested While Loop

When one while loop is living inside another while loop, it is known as nesting of while loop. It means that there are two while loops, the first one is acting as an outer loop and later one is behaving as the inner loop. Execution will take place in the manner that first the outer ‘while’ loop is triggered, then if the specified Boolean condition is matched the pointer will be passed to inner ‘while’ loop. In this too, if the Boolean condition stands to be true, the inner while loop body will be executed until specified condition does not come 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.

Syntax

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

while (condition )
    while (condition )
      # code to be executed
    end
    #expressions
end

Example 1: Print a Pattern Using Nested while Loop

We can print various patterns using nested while loops. Let us see how the following pattern can be printed.

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

num = 0

while num != 6
  j = 0
  while j != num
    print num  # Print the current value of `num` without a newline
    j += 1     # Increment the inner loop counter
  end
  puts ""      # Move to the next line after the inner loop finishes
  num += 1     # Increment the outer loop counter
end

Output

Example 2: Count Palindrome Numbers Between Two Limits Using Nested while Loop

=begin
  Ruby program to check the number of palindrome numbers
  present between two limits using nested while loop
=end

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

if ul < ll
  puts "Invalid input! Upper limit must be >= to the lower limit."
else
  while ul >= ll
    num = ul
    temp = ul
    pal = 0

    # Inner while loop to reverse the number
    while num != 0
      rem = num % 10
      num = num / 10
      pal = pal * 10 + rem
    end

    # Check if the number is a palindrome
    if temp == pal
      puts "#{temp} is a palindrome"
    end

    ul -= 1 # Decrement the upper limit to check the next number
  end
end

Output

Enter upper limit:-
200
Enter lower limit:-
10
191 is palindrome
181 is palindrome
171 is palindrome
161 is palindrome
151 is palindrome
141 is palindrome
131 is palindrome
121 is palindrome
111 is palindrome
101 is palindrome
99 is palindrome
88 is palindrome
77 is palindrome
66 is palindrome
55 is palindrome
44 is palindrome
33 is palindrome
22 is palindrome
11 is palindrome

You can observe in the above program that first the outer while loop is checked through a specified condition i.e. while loop will run until upper limit does not become equal to the lower limit.

The upper limit is passed as the number for which Palindrome check will be carried out using an inner while loop. The inner while loop has all those statements which are necessary to carry out the checking. Once, the inner evaluation is done. The pointer is going back to the outer loop and the upper limit is getting decreased by 1.

Ruby Nested For Loop

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