If [boolean condition] And [boolean condition]

[A]

Hello,

As the title says, I am trying to use the 'And' keyword in my If statement to express the result of two conditions being true. Here's my code:

Code: Pascal  [Select][+][-]

1.    If NameEdit.Text = '' And DirEdit.Text = ''
2.    Then OKButton.Enabled := False
3.    Else OKButton.Enabled := True;

This results in the following error:

unit2.pas(56,26) Error: Operator is not overloaded: "Constant String" and "TTranslateString"

I haven't a clue what this error means; am I expressing 'And' correctly? Should it be '&', '&&', or something instead?

Thank you in advance.

[skalogryz]

Code: Text  [Select][+][-]

1. If (NameEdit.Text = '') And (DirEdit.Text = '')
2.  

[A]

Thank you

[Thaddy]

Code: Pascal  [Select][+][-]

1. f (NameEdit.Text = '') And (DirEdit.Text = '')
2.  

Code: Pascal  [Select][+][-]

1. if NameEdit.Text.IsEmpty And DirEdit.Text.isEmpty // it is nearly 2018....
2.  

[skalogryz]

if NameEdit.Text.IsEmpty And DirEdit.Text.isEmpty

too glamorous!
an old-school guy here.

to be honest, I'd do it this way:

Code: Text  [Select][+][-]

1. OKButton.Enabled := (NameEdit.Text <> '') or (DirEdit.Text <> '');
2.  

but this could be a bit too complicated for beginners. (as well as it was not the question )

[Thaddy]

Rephrased above...  If i would have to express your pascal knowledge in Boolean logic it probably ends up true...

[A]

Thanks

I guess there's always more than one way of doing things.
I'll try to remember that way.
Just one last thing, is there a way of making 2 things happen If [CONDITION(S)]?

E.g.

Code: Pascal  [Select][+][-]

1.    If (NameEdit.Text = '') Or (DirEdit.Text = '')Then
2.    OKButton.Enabled := False
3.    FinalDir.Clear
4.    Else OKButton.Enabled := True;

Thank you 

[skalogryz]

Code: Pascal  [Select][+][-]

1. If (NameEdit.Text = '') Or (DirEdit.Text = '')Then begin
2.    OKButton.Enabled := False;
3.    FinalDir.Clear;
4.    end Else OKButton.Enabled := True;
5.  

[A]

Thanks. Just one last thing, I promise (sorry to be needy) but for the sake of knowledge, what does <> actually do? And when would I use it instead of '='?

Thanks for helping me out!

[skalogryz]

= equal
<> not equal

in case of

Code: Pascal  [Select][+][-]

1. NameEdit.Text <> ''
2.  

it compares the text not to be empty
(not equal to a blank string)

[A]

Good to know, thanks.

[skalogryz]

Here's another way:

Code: Pascal  [Select][+][-]

1.   OKButton.Enabled := not ( (NameEdit.Text = '') Or (DirEdit.Text = '') );
2.   if not OKButton.Enabled then FinalDir.Clear;
3.  

[A]

Thank you!

[munair]

If it comes to IF blocks Pascal can be quite confusing to those who are new to the language, probably more than any other language. Multiple conditions require parentheses. Multiple statements require begin..end and you must know when the statement closes (semicolon):

Code: Pascal  [Select][+][-]

1. If (NameEdit.Text = '') Or (DirEdit.Text = '') Then
2.   begin
3.     OKButton.Enabled := False;
4.     FinalDir.Clear;
5.   end // <- NO semicolon here
6. Else
7.   OKButton.Enabled := True; // <- end of entire IF statement
8.  

Nested IFs in particular require your attention:

Code: Pascal  [Select][+][-]

1. if condition then
2.   begin
3.     if condition then
4.       begin
5.         statement1;
6.         statement2;
7.       end; // <- nested IF block ends
8.   end // <- IF block continues
9. else if condition then
10.   begin
11.     if condition then
12.       begin
13.         statement3;
14.         statement4;
15.       end; // <- nested IF block ends
16.   end // <- IF block continues
17. else
18.   statement5; // IF block ends (single statement so BEGIN..END not necessary)

Another issue that comes up frequently is the difference between assignment (:=) and comparison (=).

[Thaddy]

Well, Munair, you missed the point: the point is that to set a boolean condition from a system of boolean conditions you do not over use if/then/else, because such a system can always be resolved using boolean math only.
Both I and skalogryz gave simple examples.

Here's your example my way:

Code: Pascal  [Select][+][-]

1. if (condition1 and condition2)  then
2.       begin
3.         statement1;
4.         statement2;
5.       end
6. else if (condition3 and condition4) then
7.       begin
8.         statement3;
9.         statement4;
10.       end else statement4;

This code will execute much faster. [I made some edits]
I can probably improve on this too:

Code: Pascal  [Select][+][-]

1. case condition of
2.    condition1 and condition2:
3.    begin
4.      statemen1;
5.      statement2;
6.   end;
7.   condition3 and condition4:
8.   begin
9.      statement3;
10.      statement4;
11.    end;
12. else
13.      statement4;
14. end;