**Course Title:** Ruby Programming: From Basics to Advanced Techniques **Section Title:** Control Structures and Functions **Topic:** Loops: while, until, for, each. ## Introduction In this topic, we will delve into the world of loops in Ruby programming. Loops are an essential part of any programming language, as they enable us to execute a block of code repeatedly, making our programs more efficient and effective. We will cover four types of loops in Ruby: `while`, `until`, `for`, and `each`. By the end of this topic, you will understand the syntax, use cases, and best practices for each type of loop. ### **1. While Loop** --------------------- A `while` loop is used to execute a block of code as long as a certain condition is true. **Syntax:** ```ruby while condition # code to be executed end ``` **Example:** ```ruby # print numbers from 1 to 5 i = 1 while i <= 5 puts i i += 1 end ``` In this example, the loop will continue to execute as long as `i` is less than or equal to 5. The `puts` statement will print the current value of `i`, and then `i` is incremented by 1 using the `+=` operator. ### **2. Until Loop** -------------------- An `until` loop is used to execute a block of code until a certain condition is true. **Syntax:** ```ruby until condition # code to be executed end ``` **Example:** ```ruby # print numbers from 1 to 5 i = 1 until i > 5 puts i i += 1 end ``` In this example, the loop will continue to execute until `i` is greater than 5. The `puts` statement will print the current value of `i`, and then `i` is incremented by 1 using the `+=` operator. ### **3. For Loop** ------------------ A `for` loop is used to execute a block of code for each element in a collection (e.g., array, hash). **Syntax:** ```ruby for variable in collection # code to be executed end ``` **Example:** ```ruby # print numbers from 1 to 5 numbers = [1, 2, 3, 4, 5] for num in numbers puts num end ``` In this example, the loop will iterate over the `numbers` array, and for each iteration, the `puts` statement will print the current value of `num`. ### **4. Each Loop** ------------------- An `each` loop is used to execute a block of code for each element in a collection (e.g., array, hash). **Syntax:** ```ruby collection.each do |variable| # code to be executed end ``` **Example:** ```ruby # print numbers from 1 to 5 numbers = [1, 2, 3, 4, 5] numbers.each do |num| puts num end ``` In this example, the loop will iterate over the `numbers` array, and for each iteration, the `puts` statement will print the current value of `num`. ### **Best Practices** -------------------- Here are some best practices to keep in mind when working with loops: * Always initialize variables before using them in a loop. * Use meaningful variable names to improve code readability. * Avoid using infinite loops (e.g., `while true`) unless absolutely necessary. * Use `break` and `next` statements to control loop flow. * Use `return` statements to exit a loop prematurely. ### **Exercise** -------------- Write a Ruby program that uses a `while` loop to print the first 10 prime numbers. **Hint:** Use the `Prime` class from the Ruby Standard Library. [Click here to learn more about the `Prime` class](https://ruby-doc.org/stdlib-2.6.3/libdoc/prime/rdoc/Prime.html). ### **Conclusion** ---------- In this topic, we covered four types of loops in Ruby: `while`, `until`, `for`, and `each`. We learned the syntax, use cases, and best practices for each type of loop. With these loops, you can write more efficient and effective Ruby programs. Do you have any questions about loops in Ruby? Feel free to leave a comment below. Next topic: **Defining and calling functions/methods.**