Practice with Loops and Algorithms

Created By: Geoffrey Challen
/ Updated: 2022-08-07

Next we'll pause to reinforce what we've learned about the basic building blocks of computer science: storing data, making decisions, and repeating operations. We'll also get some more practice with loops!

Debugging Practice

Let's warm up with a bit of graded debugging practice.


Last time we discussed how we can exit a loop early using the break statement:

break causes the enclosing loop—either while or for—to immediately exit, regardless of whether the loop condition is true or not.

continue is another control statement that we can use inside a loop. Let's explore how it works together!

Show how continue works using an example.

So while break causes the loop to exit, continue causes the code to return to the top of the loop immediately, check the loop condition, and then continue if appropriate.

continue versus if

continue is used less frequently than break. One of the reasons is that, we can always rewrite any loop that uses continue to instead use an if statement. Let's see how:

Compare continue and if.

What's more clear: continue versus an if statement? It really depends on the problem. If the loop body is long and complicated, it can be better to use continue at the beginning to avoid values that shouldn't be considered by the rest of the loop. However, overall continue can make your code hard to read. So for shorter loops, it's usually better to just put the entire loop body inside an if statement instead.

Show how to complete the homework problem above. Feel free to cover multiple approaches!

Counting Array Values

To get some additional practice, let's work through an example together that is similar to this lesson's homework. It also provides us a chance to practice with a very common array and loop programming pattern.

Given an array of values, how would we count the number of values that have some property? For example, let's say that we need to count the number of values which are greater than zero.

Solution Outline

Let's work step-by-step. First, let's outline what we need to do.

Just work through a solution outline describing the steps we'll need to take.

for Loop Setup

Next, let's get our loop set up! It's always a good idea to make sure that we can actually access all of the values in the array before doing anything more complicated.

Start with the previous solution outline and get to the point where we can print all of the values in the array.

Testing Values Using if

As the third step, let's review how we determine if a value is greater than zero, and integrate that into what we have so far.

Continue on integrating the if statement into the loop. Complete the example and test with some different arrays.

Identifying a Design Pattern

Finally, let's examine the design pattern that emerges from this example: a combination of iteration (our for loop) and selection (our if statement). By combining these two and using different conditions and data, we can solve a lot of different problems! We can also combine results in different ways as well.

Point out the general pattern that emerges from this example.

Show how to complete the homework problem above. Feel free to cover multiple approaches!

Even and Odd

Before we wrap up, let's review one useful bit of Java that we'll use regularly during some of our upcoming examples: How to test whether a value is even or odd.

Demonstrate how to use the remainder operator to test for even and odd, and what goes wrong with negative numbers.

Show how to complete the homework problem above. Feel free to cover multiple approaches!

More Practice

Need more practice? Head over to the practice page.