[Solved] How to use numeric variables in case declaration?

[loaded]

Hi All,
If we use the numeric value directly in the case statements, there is no problem, but if we use it over a numeric variable, an error occurs!

Sample code;

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2.   var
3.     i:integer=5;
4.     ib:integer=4;
5.   begin
6.     case i of
7.     0: begin
8.         end;
9.     end;
10.  
11.     case i of
12.      ib: begin  // it gives error here!!!     [Error: Constant Expression expected]
13.          end;
14.      end;
15.  end;
16. end.

Why am I getting an error like this? Is there a different setting that needs to be made?

[Red_prig]

operator case support only constant value

[howardpc]

For testing variable values you have to use a sequence of if then tests:

Code: Pascal  [Select][+][-]

1. if v = value1 then  Do1
2. else if v = value2 then  Do2
3. else if ...  etc.

[440bx]

As Red_prig stated, a case statement only supports comparisons against constants with the exception of strings.

However, there is a way to "synthesize" an inline case statement that works with variables by doing something like this:

Code: Pascal  [Select][+][-]

1. for LoopVar := 1 to 1 do  { or "for i := i to i do" but only if "i" doesn't change in the "case" statement }
2. begin
3.   { first "case" }
4.   if i = ib then
5.   begin
6.     { do whatever is appropriate when i = ib }
7.  
8.     break;
9.   end;
10.  
11.   { second case }
12.   if i = { some other variable } then
13.   begin
14.     { do whatever is appropriate in that case }
15.  
16.     break;
17.   end;
18.  
19.   { and so on until all cases are accounted for }
20. end;
21.  
22. { remaining function code follows the "for"/synthesized-case statement }

basically, the "for" loop is just a trick to create an inline scope to break out of.  The same thing can be done using a "repeat ... until TRUE".  Of course, the same thing can be accomplished by calling a function but, this way, the "case" is inline just as a normal "case" statement is.

Personally, I prefer this solution over nested "if"s which, as howardpc stated, is the more commonly used alternative.

HTH.

[loaded]

Red_prig and howardpc and 440bx Thank you very much for taking your valuable time to reply.
Topic understood!!! We keep the if expression on defense. 

[howardpc]

Since in your original example you had assigned known constant values to your variables you could also do this:

Code: Pascal  [Select][+][-]

1. procedure TForm1.Button1Click(Sender: TObject);
2. var
3.   i:integer=5;
4.   ib:integer=4;
5.   iStr: String;
6. begin
7.   iStr := i.ToString;
8.  
9.   case iStr of
10.     '0': begin
11.          end;
12.     '1': begin
13.          end;
14.     '4': DoIB;
15.     '5': DoI;
16.    otherwise      DoUnexpected;
17.   end;
18. end;

[loaded]

howardpc,Sorry we got you a little tired, it's my fault. I didn't explain my problem well at first.
The process of assigning values to variables was for exemplary purposes.They are normally changed dynamically.
Still, a good example is the tostring expression in particular. Thank you very much