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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 16 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 1

Thanks.

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

---
llegarreta@gmail.com Luis
Posted 8 years ago
 
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