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Free Pascal => General => Topic started by: CM630 on July 09, 2018, 03:31:48 pm

Title: [SOLVED] „Error: Constant and CASE types do not match‟ with string
Post by: CM630 on July 09, 2018, 03:31:48 pm

Following code works right:

Code: Pascal  [Select][+][-]

1.  
2. procedure TForm1.Button1Click(Sender: TObject);
3. var
4.   A: string='';
5.   B: string= 'B';
6.   C: string= 'C';
7. begin
8.   A:=B;
9.   case A of
10.     'B': ShowMessage (B);
11.     'C': ShowMessage (C);
12.   end;
13. end;

But this code generates „Error: Constant and CASE types do not match‟.

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. var
3.   A: string='';
4.   B: string= 'B';
5.   C: string= 'C';
6. begin
7.   A:=B;
8.   case A of
9.     B: ShowMessage (B);
10.     C: ShowMessage (C);
11.   end;
12. end;

B and C are strings. I tryed to cast to cast them to strings, anyway, but still I get the same error?
Is it me doing sth. wrong?

Title: Re: „Error: Constant and CASE types do not match‟ with string
Post by: RayoGlauco on July 09, 2018, 03:49:09 pm

In the second example, you use variables as selectors, instead of constants (B is a variable; 'B' is a constant). You cannot use variables as selectors.

See http://wiki.freepascal.org/Case (http://wiki.freepascal.org/Case)

Title: Re: „Error: Constant and CASE types do not match‟ with string
Post by: Thaddy on July 09, 2018, 03:50:04 pm

Needs a literal value, indeed.

Title: Re: „Error: Constant and CASE types do not match‟ with string
Post by: Gammatester on July 09, 2018, 03:50:20 pm

You should read the second part of the error message 'Error: String expression expected'. The case labels must be constants (i.e. literals or true constants). Your construct would throw equivalent message even for integer variables. The following code does work:

Code: Pascal  [Select][+][-]

1. var
2.   A: string='';
3. const
4.   B = 'B';
5.   C = 'C';
6. begin
7.   A:=B;
8.   case A of
9.     B: writeln (B);
10.     C: writeln (C);
11.   end;
12. end;
13.  

Title: Re: „Error: Constant and CASE types do not match‟ with string
Post by: CM630 on July 09, 2018, 03:57:15 pm

Ok, thanks, I will rewrite it with

Quote

If... then.