RC2 bug? No [Solved]

[bobc50]

I wanted to make programs more maintainable. I created coded with same structure as below. My intent is to execute one of two while loops based on a condition. The code, other than the while statement is identical for both.

The code below compiles and, IMHO, is a clear representation of what I want to do. If I set a breakpoint at the start and single step the program goes off the deep end on the
"while I = 0" do statement and appears to simply hang.

• Is that a Lazarus bug and, if so, how do I report it?
• I worked around this problem by repeating the code starting with the begin line with the comment to the end statement in a straightforward way. It is possible that I can make the code between that begin end another function. What is the suggested approach?

Code: Pascal  [Select][+][-]

1.    
2. program project1;
3. var
4.   i: integer;
5.   b: boolean;
6. begin
7.   i := 0;
8.   b := true;
9.   if b = true then
10.     while i = 0 do
11.   else
12.     while i = 1 do
13.     begin // this code might be quite long
14.       i := (i + 1) mod 2
15.     end;
16. end.
17.  

   

[wp]

the "while I = 0" do statement and appears to simply hang.

You do not provide a condition for terminating the loop.

[EDIT]
Sorry - this is expressed badly. The correct words should be: You do not change i inside the while loop so that the initial condition (i=0) always remains true.

[bobc50]

the "while I = 0" do statement and appears to simply hang.

You do not provide a condition for terminating the loop.

Thanks, but I don't understand. I'm still learning Pascal, but isn't i = 0 a condition? The following code compiles and executes with no issue. Can I rewrite my original code without making two copies of the stuff I want to execute when the initial conditon is meet?

program project1;
var
  i: integer;
  b: boolean;
begin
  i := 0;
  b := true;
  if b = true then
    while i = 0 do
    begin // some stuff
      i := (i + 1) mod 2;
      writeln(i);
    end
  else
    while i = 1 do
    begin // a copy of the stuff
      i := (i + 1) mod 2;
      writeln(i);
    end;
end.

[Martin_fr]

Well the "while i = 0" will run forever.

Your code is the same as the following (with extra begin end for more clarity)

Code: Pascal  [Select][+][-]

1. program project1;
2. var
3.   i: integer;
4.   b: boolean;
5. begin
6.   i := 0;
7.   b := true;
8.   if b = true then
9.   BEGIN
10.     while i = 0 do
11.        {empty statement};
12.   END
13.   else
14.   BEGIN
15.     while i = 1 do
16.     begin // this code might be quite long
17.       i := (i + 1) mod 2
18.     end;
19.   END;
20. end.
21.    

Since "b=true" the first loop, with the "empty statement" is executed. And since "i=0" and i never changes, that loop runs forever.

If you are in the debugger, you can use pause to interrupt => however, (OS dependent), pause may create a temporary thread, in which case you must open the thread window and switch to your main thread.

[Martin_fr]

Please use "code tags"

Ah...

No, you can't "detach" the "while" from the code that runs in the while. (you can't have 2 while conditions for a single loop-code).

But you can

Code: Pascal  [Select][+][-]

1. if b then
2.   ConditionVal := 1
3. else
4.   ConditionVal := 0;
5. while c = ConditionVal do begin
6. // ....
7. end;

[Martin_fr]

Mind, in Pascal the semicolon ";" is a statement separator.

So for the last statement before an "end" you do not need a semicolon (but for various reasons, better put it there).

"ELSE" also terminates the ("else sub-") statement (and in front of else you are not allowed a semicolon).

So that is why your first "while" loop ends at the "else". And because you have nothing between "do else", the while loop executes an "empty statement".

[bobc50]

Thanks to all for your help. I understand where I went wrong. I will use the approach suggested by Martin_fr.