Ruby Nested Do While Loop

By IncludeHelp Last updated : November 16, 2024

Nested do...while loop

When two post-test loops i.e. do..while loops are working together for the fulfillment of a task, it is known as the nesting of the do...while loop. It, means that there are two do-while loops, first one is behaving as an outer loop and later one is acting as an inner loop. Execution of both the loops will take place in the way that first, the pointer will work with the outer loop then it will move to the inner loop as the condition is checked after the execution of the block. Again inside the block will be executed and then the condition will be checked and then the pointer will move to the outer loop for checking the specified Boolean condition of the outer loop. In this loop, both the blocks will be executed at least for once because do-while is an exit-control loop.

Syntax

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

loop do
    # code block
    loop do
      # code block
      break if Condition
    end
    break if Condition
end

Example 1: Count Armstrong Numbers Between Two Limits Using Nested do-while Loops


=begin
  Ruby program to check the number of Armstrong numbers
  present between two limits using a nested do-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
  loop do
    num = ul
    temp = ul
    arm = 0

    # Inner loop to calculate the sum of cubes of digits
    loop do
      rem = num % 10
      num = num / 10
      arm = arm + rem * rem * rem
      break if num == 0
    end

    # Check if the number is an Armstrong number
    if temp == arm
      puts "#{temp} is an Armstrong number"
    end

    ul -= 1  # Decrement the upper limit to move to the next number
    break if ul < ll  # Exit the loop when the range is complete
  end
end

Output

Enter upper limit:-
1000
Enter lower limit:-
100
407 is armstrong
371 is armstrong
370 is armstrong
153 is armstrong

Example 2: Count and Print Palindrome Numbers Between Two Limits Using Nested Loops


=begin
  Ruby program to check and count the number of palindrome numbers
  present between two limits using a nested do-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 >= the lower limit."
else
  palindrome_count = 0

  loop do
    num = ul
    temp = ul
    pal = 0

    # Inner loop to reverse the digits of the number
    loop do
      rem = num % 10
      num = num / 10
      pal = pal * 10 + rem
      break if num == 0
    end

    # Check if the number is a palindrome
    if temp == pal
      puts "#{temp} is a palindrome"
      palindrome_count += 1
    end

    ul -= 1  # Decrement the upper limit to move to the next number
    break if ul < ll  # Exit the loop when the range is complete
  end

  puts "Total palindrome numbers found: #{palindrome_count}"
end

Output

Enter upper limit:-
200
Enter lower limit:-
100
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

In the above examples, you can observe that two do-while loops are working together to find the palindrome and Armstrong series between two ranges or limits. The outer do-while loop is working to decrease the upper limit by one so that the loop could work between those two specified numbers. The inner loop is processing each number to check whether it is palindrome/Armstrong or not.

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