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   ► KBProgrammingDelphi for W...Language Det...   Print This     
  From the June 2011 Issue of Prestwood eMag
 
Delphi Language Details:
Using Case Statements in Object PASCAL
 
Posted 22 years ago on 3/13/2003 and updated 1/17/2011
Take Away: Using case statements in Delphi.

KB100132

Instead of using a bunch of complex nested if statements, you can use a case statement to provide a more readable alternative so long as the conditionals return an integer.

Case Syntax:
case selectorExpression of
 caseList1: statement1;
 ...
 caseListx: statementx;
end

The selectorExpression is any expression of an ordinal type. This can be a number like 1, 2, 3, etc., an expression that evaluates to an ordinal, or a constant (like Red, White, and Blue). Unfortunately string types are not valid. (ObjectPAL programmers will note that ObjectPAL's switch statement is much more powerful and easier to use.)

Here is a simple example of using a case statement. 
// Set x to 1, 2, 3, then 4 to see what
// message is displayed.
procedure TForm1.Button2Click(Sender: TObject);
var
 lbValue: Byte; // Local byte (lb).
begin
 lbValue := 3;
 case lbValue of
  1: ShowMessage('one');
  2: ShowMessage('two');
  3: ShowMessage('three');
 else
  ShowMessage('special');
 end;
end;
Using Case and MessageBox

In this next example, we use the fact that MessageBox returns an integer. What integer it returns is based on what button the user chooses. Refer to the code below for integer values:

procedure TForm1.Button3Click(Sender: TObject);
var
 liAns: Integer; // Local integer (li).
begin
 liAns := Application.MessageBox('Are you a Delphi fan?', 
  'Yes or No?', MB_YesNoCancel);
 case liAns of
  2: ShowMessage('You chose Cancel');
  6: ShowMessage('You chose Yes.');
  7: ShowMessage('You chose No.');
 end;
end;

Comments

1 Comments.
Share a thought or comment...
Comment 1 of 2

Thanks.

I was confused aout the else syntax. It turns out I was missing a quote

---
llegarreta@gmail.com Luis
Posted 14 years ago

Comment 2 of 2

A case statement is a programming language command that can be used in Object PASCAL to select which subroutine should execute top writing services, based on the value of one or more expressions. Case statements are often used when writing nested loops and if/then/else clauses. The operator "case" selects which branch will execute depending on the value of an expression.

Posted 42 months ago
 
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KB Post Contributed By Mike Prestwood:

Mike Prestwood is a drummer, an author, and creator of the PrestwoodBoards online community. He is the President & CEO of Prestwood IT Solutions. Prestwood IT provides Coding, Website, and Computer Tech services. Mike has authored 6 computer books and over 1,200 articles. As a drummer, he maintains play-drums.com and has authored 3 drum books. If you have a project you wish to discuss with Mike, you can send him a private message through his PrestwoodBoards home page or call him 9AM to 4PM PST at 916-726-5675 x205.

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