do...while Repetition Statement

The do...while repetition statement is similar to the while statement. In the while, the application tests the loop-continuation condition at the beginning of the loop, before executing the loop's body. If the condition is false, the body never executes. The do...while statement tests the loop-continuation condition after executing the loop's body; therefore, the body always executes at least once. When a do...while statement terminates, execution continues with the next statement in sequence. Figure 6.7 uses a do...while (lines 1115) to output the numbers 110.

Figure 6.7. do...while repetition statement.

 1 // Fig. 6.7: DoWhileTest.cs
 2 // do...while repetition statement.
 3 using System;
 5 public class DoWhileTest
 6 {
 7 public static void Main( string[] args )
 8 {
 9 int counter = 1; // initialize counter
11 do 
12 { 
13  Console.Write( "{0} ", counter ); 
14  counter++; 
15 } while ( counter <= 10 ); // end do...while
17 Console.WriteLine(); // outputs a newline
18 } // end Main
19 } // end class DoWhileTest
1 2 3 4 5 6 7 8 9 10

Line 9 declares and initializes control variable counter. Upon entering the do...while statement, line 13 outputs counter's value, and line 14 increments counter. Then the application evaluates the loop-continuation test at the bottom of the loop (line 15). If the condition is true, the loop continues from the first body statement in the do...while (line 13). If the condition is false, the loop terminates, and the application continues with the next statement after the loop.

Figure 6.8 contains the UML activity diagram for the do...while statement. This diagram makes it clear that the loop-continuation condition is not evaluated until after the loop performs the action state at least once. Compare this activity diagram with that of the while statement (Fig. 5.4). It is not necessary to use braces in the do...while repetition statement if there is only one statement in the body. However, most programmers include the braces, to avoid confusion between the while and do...while statements. For example,

while ( condition )

is normally the first line of a while statement. A do...while statement with no braces around a single-statement body appears as:

while ( condition );

which can be confusing. A reader may misinterpret the last linewhile( condition );as a while statement containing an empty statement (the semicolon by itself). Thus, a do...while statement with one body statement is usually written as follows:

} while ( condition );

Figure 6.8. do...while repetition statement UML activity diagram.

Error Prevention Tip 6 4

Always include braces in a do...while statement, even if they are not necessary. This helps eliminate ambiguity between while statements and do...while statements containing only one statement.

switch Multiple Selection Statement



    Introduction to Computers, the Internet and Visual C#

    Introduction to the Visual C# 2005 Express Edition IDE

    Introduction to C# Applications

    Introduction to Classes and Objects

    Control Statements: Part 1

    Control Statements: Part 2

    Methods: A Deeper Look


    Classes and Objects: A Deeper Look

    Object-Oriented Programming: Inheritance

    Polymorphism, Interfaces & Operator Overloading

    Exception Handling

    Graphical User Interface Concepts: Part 1

    Graphical User Interface Concepts: Part 2


    Strings, Characters and Regular Expressions

    Graphics and Multimedia

    Files and Streams

    Extensible Markup Language (XML)

    Database, SQL and ADO.NET

    ASP.NET 2.0, Web Forms and Web Controls

    Web Services

    Networking: Streams-Based Sockets and Datagrams

    Searching and Sorting

    Data Structures



    Appendix A. Operator Precedence Chart

    Appendix B. Number Systems

    Appendix C. Using the Visual Studio 2005 Debugger

    Appendix D. ASCII Character Set

    Appendix E. Unicode®

    Appendix F. Introduction to XHTML: Part 1

    Appendix G. Introduction to XHTML: Part 2

    Appendix H. HTML/XHTML Special Characters

    Appendix I. HTML/XHTML Colors

    Appendix J. ATM Case Study Code

    Appendix K. UML 2: Additional Diagram Types

    Appendix L. Simple Types


    Visual C# How to Program
    Visual C# 2005 How to Program (2nd Edition)
    ISBN: 0131525239
    EAN: 2147483647
    Year: 2004
    Pages: 600 © 2008-2020.
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