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


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?