Programming Fundamentals/Loops/Do Loops

A do while loop is a control flow statement that executes a block of code at least once, and then repeatedly executes the block, or not, depending on a given Boolean condition at the end of the block. This activity introduces do loops. This activity will help you understand how to use do loops in a program.

Objectives

• Understand do loop concepts.
• Understand how do loops are specified in a program.
• Understand the difference between while loops and do loops and when to use each one.
• Single-step through a program to observe do loop execution.

Prerequisites

Learners should already be familiar with while loops.

Introduction

Flowgorithm do loop

Review the flowchart example on the right.

Questions

• What flowcharting symbol is used to indicate a do loop?
• How are do loops structured?
• What is the difference between a while loop and a do loop?
• When would you want to use a while loop vs. a do loop?

Activity

With a partner, perform the following:

1. Using a visual programming language, create a program similar to the flowchart on the right based on the following steps.
2. Start by creating a do loop that counts from 1 to 5 by 1.
3. Save the program.
4. Test the program to verify that it works correctly.
5. Modify the program to count from 1 to 10 by 1.
6. Modify the program to count from 5 to 10 by 1.
7. Modify the program to count from 0 to 10 by 2.
8. Trade places, so that both partners have an opportunity to "drive" the visual programming environment.
9. Modify the program to count from any start value the user enters to 10 by 1.
10. Modify the program to count from any start value the user enters to any stop value the user enters by 1.
11. Modify the program to count from any start value the user enters to any stop value the user enters by any increment value the user enters.
12. Change the environment to use a slow run speed and/or step through the program one shape at a time.
13. Working together, create a list of changes that might be made to use do loops in programs you've already written. What parts could be repeated and how would the loop terminate?

Applications

• Identify specific steps which must be followed when creating a program using do loops.
• Discuss your activity experience with your classmates. What surprised you? What have you learned that you can apply to your own school or work environment?