DO UNTIL

Tools for Structured and Object-Oriented Design

Objectives

• Indentify, and use in program design, the DO UNTIL control Structure

• Distinguish between the logic of a DOWHILE pattern and the logic of a DOUNTIL pattern.

Using the Do Until Loop

• When you use either a while or a for loop, the body of the loop may never execute

• When you want to ensure that a loop’s body executes at least one time, you can use a do until loop

• In a do until loop, the loop control variable is evaluated after the loop body executes

• Therefore, the body always executes at least one time

do until Loop for Producing One Extra Label

Printing One Label, Then Printing Enough to Cover Production

Recognizing the Characteristics Shared by All Loops• All structured loops share these characteristics:

– The loop-controlling question provides either entry to or exit from the repeating structure

– The loop-controlling questions provide the only entry to or exit from the repeating structure

• You should also notice the difference between unstructured loops and the structured do until and while loops

DO UNTIL Example

DO UNTIL Example

DO UNTIL ExamplePseudocode

DO UNTIL Example

DO UNTIL Example

DO UNTIL Examples

DOWHILE vs. DOUNTIL

DOWHILE vs. DOUNTIL