Control Flow: Conditionals and Loops

In Ruby, control flow structures allow you to execute different code depending on certain conditions or iterate over collections of data. Mastering conditionals and loops is key to writing dynamic programs that respond to different inputs.

In this lesson, you will learn:

• How to use conditional statements to make decisions in your programs.
• How to loop through data with various types of loops.
• The differences between if statements, case statements, and different looping mechanisms in Ruby.

Main Concepts in Ruby: Control Flow

1. If, Else, Elsif Statements:

   • The most common control flow structure in Ruby. if evaluates an expression and executes the code block if the condition is true. else handles cases when the condition is false. elsif allows checking multiple conditions.

   age = 18
   if age >= 18
     puts 'Adult'
   elsif age < 18
     puts 'Minor'
   else
     puts 'Invalid age'
   end
   

2. Case Statements:

   • Ruby’s case statement is a clean way to handle multiple conditions. It’s often used when you have many options to check.

   grade = 'A'
   case grade
   when 'A'
     puts 'Excellent'
   when 'B'
     puts 'Good'
   when 'C'
     puts 'Average'
   else
     puts 'Invalid grade'
   end
   

3. While Loop:

   • A while loop runs as long as the specified condition is true.

   count = 0
   while count < 5
     puts count
     count += 1
   end
   

4. For Loop:

   • The for loop is used to iterate over a collection of values, such as an array or range.

   for i in 1..5
     puts i
   end
   

5. Each Loop:

   • Ruby’s each method is an elegant way to loop through collections like arrays or hashes.

   arr = [1, 2, 3, 4]
   arr.each do |num|
     puts num
   end
   

Practical Applications of Ruby Control Flow

Task: Determine Voting Eligibility

1. Write a Ruby script that checks if a user is eligible to vote based on their age.

   print 'Enter your age: '
   age = gets.chomp.to_i
   if age >= 18
     puts 'You are eligible to vote.'
   else
     puts 'You are not eligible to vote.'
   end
   

Task: Calculate Even or Odd Numbers

1. Create a program that takes a number as input and checks if it’s even or odd.

   print 'Enter a number: '
   num = gets.chomp.to_i
   if num % 2 == 0
     puts 'Even'
   else
     puts 'Odd'
   end
   

Task: Display Grade Based on Score

1. Write a program using a case statement to print a grade based on the score.

   print 'Enter score: '
   score = gets.chomp.to_i
   case score
   when 90..100
     puts 'A'
   when 80..89
     puts 'B'
   when 70..79
     puts 'C'
   else
     puts 'F'
   end
   

Task: Loop through an Array

1. Use a for loop to display the elements of an array.

   fruits = ['apple', 'banana', 'cherry']
   for fruit in fruits
     puts fruit
   end
   

Task: Sum Elements in an Array

1. Use an each loop to find the sum of all elements in an array.

   numbers = [1, 2, 3, 4, 5]
   sum = 0
   numbers.each do |num|
     sum += num
   end
   puts sum  # Output: 15
   

Advanced Insights into Ruby Control Flow

1. Efficient Looping:

   • Ruby's each loop is more efficient and readable compared to traditional for loops, especially when working with collections like arrays and hashes.
   • You can also use each_with_index to iterate with index in arrays.

   arr = ['a', 'b', 'c']
   arr.each_with_index do |value, index|
     puts "#{index}: #{value}"
   end
   

2. Infinite Loops:

   • Be cautious when using while loops, as they can lead to infinite loops if the condition is always true.

   loop do
     puts 'This will run forever'
   end
   

3. Using next and break:

   • next allows you to skip to the next iteration of a loop, while break allows you to exit a loop prematurely.

   (1..5).each do |i|
     next if i == 3
     puts i
   end
   # Output: 1, 2, 4, 5
   

4. Combining Conditionals with Loops:

   • You can combine control flow statements to solve complex problems, such as filtering values during iteration.

   numbers = [1, 2, 3, 4, 5]
   numbers.each do |num|
     break if num == 4
     puts num
   end
   

Additional Resources for Ruby Control Flow

• Ruby Control Flow Documentation: Ruby Docs
• Ruby Loops and Iterators: Ruby Iterators
• Ruby: The Official Guide: Ruby Guides

Explore these resources to understand more about Ruby's control flow mechanisms and to practice using them in your programs.