What is A Loop? A loop lets you repeat an action many times. The Ruby Each Loop The Ruby method each allows you to go over a list of items, without having to keep track of the number of iterations, or having to increase some kind of counter. There are different ways to do this depending on the situation. Remember that the index starts at 0. The Times Loop This is the easiest loop you can work with. Look at this code : But what if you want the number? You can also do that with times. Example : Give it a try!
Range Looping You may have noticed that when using the times method it starts counting from 0. This can be a bit inconvenient if you want to start with a different number. An infinite loop! Ruby Until Loop There is another keyword, until , which is the same as while but the condition is reversed. Other languages use the continue statement. In Ruby, we use next. You could do something like this : This also works for while loops. In this chapter of Ruby Essentials we will look at using while and until structures to allow loops to be built into applications.
In the next chapter we will look at using the for loop and Ruby looping methods. In the above outline, expression is a Ruby expression which must evaluate to true or false. The ruby code here marker is where the code to executed is placed.
This code will be repeatedly executed until the expression evaluates to false. The above code will output the value of i until i is no longer less than 5, resulting in the following output:. It is sometimes necessary to break out of a while loop before the while expression evaluates to false. This can be achieved using the break if statement:. Ruby's until statement differs from while in that it loops until a true condition is met.
For example:. The unless statement provides an alternative mechanism to the if else construct. For example we might write an if else statement as follows:. In this chapter of Ruby Essentials we have looked in detail at creating loops that depend on specific criteria. This essentially involved the use of while and until statements.
In the next chapter we will look at using the for loop and Ruby looping methods. In the above outline, expression is a Ruby expression which must evaluate to true or false. The ruby code here marker is where the code to executed is placed. This code will be repeatedly executed until the expression evaluates to false. The above code will output the value of i until i is no longer less than 5, resulting in the following output:.
It is sometimes necessary to break out of a while loop before the while expression evaluates to false. This can be achieved using the break if statement:. Ruby's until statement differs from while in that it loops until a true condition is met. For example:. The unless statement provides an alternative mechanism to the if else construct. For example we might write an if else statement as follows:. In this chapter of Ruby Essentials we have looked in detail at creating loops that depend on specific criteria.
This essentially involved the use of while and until statements. In the next chapter we will look at Looping with for and the Ruby Looping Methods. As you can see, even though y is initialized in the body of the while loop, it's still in scope after the loop finishes running.
We didn't mention the until loop in the introduction paragraph. We do, however, need to mention them briefly so that you know about them. The until loop is simply the opposite of the while loop. You can substitute it in order to phrase the problem in a different way.
Let's look briefly at how it works. There are instances when using until will allow you to write code that is more readable and logical. Ruby has many features for making your code more expressive. The until loop is one of those features. As with while loops, until is not a method. Therefore, until loops do not have their own scope. Let's write some code that asks if the user wants to perform an action again, but we'll keep prompting the user to enter 'Y' until they do.
Notice that we're using a simple loop with out break condition at the end of the loop, therefore ensuring that the loop executes at least once. Try copying and pasting the above code into irb and playing with it. Compare this with a normal "while" loop. In Ruby, for loops are used to loop over a collection of elements.
Unlike a while loop where if we're not careful we can cause an infinite loop, for loops have a definite end since it's looping over a finite number of elements. It begins with the for reserved word, followed by a variable, then the in reserved word, and then a collection of elements. We'll show this using an array and a range. A range is a special type in Ruby that captures a range of elements.
For example The odd thing about the for loop is that the loop returns the collection of elements after it executes, whereas the earlier while loop examples return nil. Let's look at another example using an array instead of a range. In this case, we had to reverse the array to ensure a proper countdown. Otherwise, the loop would have counted up.
You can see there are a lot of ways to loop through a collection of elements using Ruby. Let's talk about some more interesting ways you can use conditions to modify the behavior of your loops. Most Rubyists forsake for loops and prefer using iterators instead. We'll cover iterators later. As with the while and until loops, for is not implemented as a method. Therefore, a for loop does not have its own scope -- the entire body of the loop is in the same scope as the code that contains the for loop.
To make loops more effective and precise, we can add conditional flow control within them to alter their behavior. Let's use an if statement in a while loop to demonstrate. This loop uses the odd? If it is, it prints to the screen. Next, x increments by one, and then the loop proceeds to the next iteration. If you place the next reserved word in a loop, it will jump from that line to the next loop iteration without executing the code beneath it.
If you place the break reserved word in a loop, it will exit the loop immediately without executing any more code in the loop. We use the next reserved word here to avoid printing the number 3 in our loop. Let's try break as well. When you run this program you can see that the entire loop exits when the value of x reaches 7 in the loop. That is why the print out only goes to 5. Loops are basic constructs in any programming language, but most Rubyists, where possible, prefer iterators over loops.
We'll talk about iterators next. Iterators are methods that naturally loop over a given set of data and allow you to operate on each element in the collection. We said earlier that arrays are ordered lists. Let's say that you had an array of names and you wanted to print them to the screen. How could you do that? You could use the each method for arrays, like this:. We have called the each method using the dot operator.
What this method does is loop through each element in our array, in order, starting from 'Bob'. Then it begins executing the code within the block. Each time we iterate over the array, we need to assign the value of the element to a variable. In this example we have named the variable name and placed it in between two pipes. After that, we write the logic that we want to use to operate on the variable, which represents the current array element.
In this case it is simply printing to the screen using puts. A block is just some lines of code ready to be executed. When working with blocks there are two styles you need to be aware of. We use the words do and end when we are performing multi-line operations. We've added the counter x to add a number before each name, creating a numbered list output.
The number x is incremented every time we go through the iteration. Memorizing these small differences in syntax is one of the necessary tasks a Ruby programmer must go through. Ruby is a very expressive language. Part of what makes that possible is the ability to do things in more than one way. There are many other iterator methods in Ruby, and over time, you'll get to use a lot of them. For now, know that most Rubyists prefer to use iterators, like the each method, to loop over a collection of elements.
Before starting this section on Recursion, you may want to review the material on the call stack from the Methods chapter. Understanding the call stack will help you better understand recursion. Recursion is another way to create a loop in Ruby.
Recursion is the act of calling a method from within itself. That probably sounds confusing so let's look at some actual code to get a better idea. Let's say you wanted to know what the double of a number was, then the double of that number, etc. Let's say you wanted to double the number until the pre-doubled number is 10 or greater. You could create the following method:. This version of the method calls the doubler method again, passing it the doubled version of the value stored in the start variable.
Once again, here is the declaration and use of the method using irb:. We are using a method that uses recursion to calculate the nth number in the fibonacci sequence. You can learn more about the fibonacci sequence here.
We have a negative statement, which we try to avoid because it makes the logic harder to understand. The key here is the next keyword, which skips to the next loop iteration, which is a number in this example. You can also break out of a loop early, before the condition is met, or before you go over all the elements of the collection.
With all of these methods you NEVER have to use the for loop, which is a useless remnant from other languages. Quick Navigation What is A Loop? Ruby While Loop. What is A Loop? A loop lets you repeat an action many times. The Ruby Each Loop The Ruby method each allows you to go over a list of items, without having to keep track of the number of iterations, or having to increase some kind of counter. There are different ways to do this depending on the situation. Remember that the index starts at 0.
The Times Loop This is the easiest loop you can work with. Look at this code : But what if you want the number? You can also do that with times. Example : Give it a try! Range Looping You may have noticed that when using the times method it starts counting from 0.
This can be a bit inconvenient if you want to start with a different number. But there is a more efficient way to write this loop. By using a while loop, we can make our code cleaner and simpler. A while loop is a loop statement that will be run when a boolean expression is true.
For example, a while loop may be run until a counter reaches 10, or until another condition is met. The while loop will stop as soon as the boolean expression is equal to false. On the first line, we define a counter variable, i. Then, on the next line, we create a while loop that will run until our counter is equal to five.
As soon as our counter reaches 5 , the boolean expression will become false , and our program will stop. Then, on the next line, our program adds one to our counter, and then the program prints out our counter. Finally, as soon as the loop has been executed five times, the loop stops because i becomes equal to five , and so our conditional is false. But before i is equal to five, our conditional statement is true which means our loop runs.
Thus, after i reaches five our final statement, The counter is complete. Until loops, the opposite of the while loop, are not as common in practice but can be useful in some situations. As you can see, our program runs until i is greater than 5 , after which point the program breaks and moves onto the next line of code.
While loops allow you to perform an action while a certain expression is equal to true. In this tutorial, we have discussed the basics of loops in Ruby. About us: Career Karma is a platform designed to help job seekers find, research, and connect with job training programs to advance their careers.
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You will learn while loop in this chapter. Initially, the value i is 1. Then we add 10 to 'i' and assign the 'sum' to 'i', thus making the value of i equal to '20'. Now you are ready to learn loops. A loop is same as its name. It repeats the codes inside its body to a fixed number of times not necessarily. Let's see an example of while loop to print the multiplication table of 14 on screen:. A loop will run till its condition is getting sattisfied or the condition is true.
This means that the codes inside the while loop will repeat if 'i' is less than or equal to Initially, 'i' is 1. Again the condition of while loop gets satisfied, since the value of 'i' is 2 this time 2 is less than So now you know that in the above example, the while loop will stop when i becomes greater than The code inside the body of while is simple.
It is taking marks as input and calculating the percentage and printing it on the screen. After printing the total marks and percentage, again the user is asked to press 'y' or 'n' depending on whether the user wants to calculate more or not. But if the user enters 'y', then there will be no effect on the variable more , and the loop will be executed again.
The above 'while' will run till 'more' is true and it can change if we don't give 'y' to 'a'. And if we enter 'y', then whole loop will run again because 'more' is not changed and is still true. Whenever a loop encounters 'break', it just stops there and executes the rest of the code written after the loop.
See this example to understand it more clearly. This means that the loop will run forever infinite loop. To stop this, we can use break and we have used it. Any other statement of the loop will not be further executed.
It is that simple. The remaining code is just the same as used in the previous example. Nesting means having one loop inside another. It means to have a loop inside the body of other loop. You have already studied about having one if under another, it is also similar. Let's see an example first. In the first iteration of the outer while loop, a is 1 and the inner while loop is inside the body of the outer while loop. Again the condition of inner while loop will be checked but it will be found false since the value of b is 6.
Now, the second iteration of the outer while will occur but since a is 0, so its condition is also false. So, it will also stop. In short, there is nothing new in nesting of loops. Inner loop is like the other statements of a loop, after executing once, it will be completed first and then the rest of the statements of the outer loop will be executed. Let's have a look on one more example on this:. Try to understand this example yourself. Just go step by step with every while loop and you will understand this.
Though this is not graphical but we will construct the working structure. You can learn to link graphics to this or any game after completing this course. For example, a program that prints all of your new email will need to print each email from a list, not just a single email. To do this, constructs called loops are used. A loop will repeat the statements inside it a number of times until some condition is met.
The first type of these loops is a while loop. While loops will execute all of the statements contained within them as long as the conditional statement remains true. In this example, the loop continually increases the value of the variable i by one. Until loops are almost identical to while loops except that they will loop as long as the conditional statement is false. The while loop will loop while the condition is true, the until loop will loop until the condition is true. The variable is incremented by one until its value equals ten.
Though the more traditional while and until loops are used in Ruby programs, closure-based loops are more common. It isn't even necessary to understand what closures are or how they work in order to use these loops; in fact, they're viewed as normal loops despite being very different under the hood.
The times loop can be used on any variable containing a number or used on a number itself. In the following example, the first loop is run 3 times and the second loop is run however many times is input by the user. If you input 12, it would run 12 times. You'll notice that the times loop uses the dot syntax 3. This has to do with how the times loop works under the hood but it's used in the same way a while or until loop is used.
The each loop is perhaps the most useful of all the loops. Each loop will take a list of variables and run a block of statements for each of them.
James Gallagher is a self-taught researcher at Career Karma, publishing comprehensive reports on the bootcamp. He also serves as a is the argument to the the programming language. The first time the loop runs, the n variable will job seekers find, research, and variable name in pipe characters,or money-back guarantees. Java Examples Java 8 Java 11 Java HTML 5 Interactive. Learn about the CK publication. PARAGRAPHAbout us: Career Karma is variable the loop is looking at is assigned to the second time the loop runs which is n in the. One thing to note here programmer and the technical content array nums and storing it. Using this we can also programmer specializing in Linux and. Career Karma matches you with way to create a loop loop's block of statements.The simplest way to create a loop in Ruby is using. Ruby - Loops Loops in Ruby are used to execute the same block of code a specified number of times. This chapter details all the loop statements supported by. Ruby | Loops (for, while, aunn.essaywritingspot.com, until) Looping in programming languages is a feature which clears the way for the execution of a set of.