This snippet not only causes a runtime error, it makes FPC close if I run it using the debugger.
procedure sortplayersbyscore(var vAux:tplayers);
procedure swap(var a:trplayers;var b:trplayers);
var
rAux:trplayers;
begin
rAux:=a;
a:=b;
b:=rAux;
end;
var
i,j:integer;
sorted:boolean;
begin
vAux:=playersarray;
i:=1;
sorted:=false;
while (i <= MAXPLAYERS -1) and not sorted do
begin
j:=1;
sorted:=true;
while (j <= MAXPLAYERS -i) do
begin
if (vAux[j].score < vAux[j+1].score) then
begin
swap(vAux[j],vAux[j+1]);
sorted:=false;
end;
inc(j);
end;
inc(i);
end;
end;
The code itself is part of a really big source file, I can post the whole thing but the responsible for the error is just that bunch of lines. The debugger terminates at line:
swap(vAux[j],vAux[j+1]);
tplayers is just a type defined as an array of records that contain score (an integer) among a bunch of other variables. trplayers is the type of the aforementioned records. I'm at a total loss; FPC (while not under debugging mode) spits an out-of-range error but under my watches I see that the variables I'm trying to read exist. Any help is really appreciated!
rAux:trplayers; have you typed a wrong symbol or the type here really contains "r" in its name?
It looks valid (other than typos) ... so let's try something simple.
What's the value of "j" when you abort?
If the debugger won't tell you, try adding:
writeln ('j = ', j);
just before the "swap" call.
As Yochai's question implied, your array needs to be dimensioned at least from
1 (or lower) to MAXPLAYERS (or larger). (I.e.: 0..MAXPLAYERS-1 would not work,
but 1..MAXPLAYERS should.)
Related
It has been around 20 years since I last had to write in Pascal. I can't seem to use the structure elements of the language correctly where I am nesting if then blocks using begin and end. For example this gets me an Compiler Error "Identifier Expected".
procedure InitializeWizard;
begin
Log('Initialize Wizard');
if IsAdminLoggedOn then begin
SetupUserGroup();
SomeOtherProcedure();
else begin (*Identifier Expected*)
Log('User is not an administrator.');
msgbox('The current user is not administrator.', mbInformation, MB_OK);
end
end;
end;
Of course if I remove the if then block and the begin end blocks associated with them then everything is OK.
Sometimes I get it this kind of syntax right and it works out OK, but the problems become exasperated when nesting the if then else blocks.
Solving the problem is not enough here. I want to have a better understanding how to use these blocks. I am clearly missing a concept. Something from C++ or C# is probably creeping in from another part of my mind and messing up my understanding. I have read a few articles about it, and well I think I understand it and then I don't.
You have to match every begin with an end at the same level, like
if Condition then
begin
DoSomething;
end
else
begin
DoADifferentThing;
end;
You can shorten the number of lines used without affecting the placement, if you prefer. (The above might be easier when you're first getting used to the syntax, though.)
if Condition then begin
DoSomething
end else begin
DoADifferentThing;
end;
If you're executing a single statement, the begin..end are optional. Note that the first condition does not contain a terminating ;, as you're not yet ending the statement:
if Condition then
DoSomething
else
DoADifferentThing;
The semicolon is optional at the last statement in a block (although I typically include it even when it's optional, to avoid future issues when you add a line and forget to update the preceding line at the same time).
if Condition then
begin
DoSomething; // Semicolon required here
DoSomethingElse; // Semicolon optional here
end; // Semicolon required here unless the
// next line is another 'end'.
You can combine single and multiple statement blocks as well:
if Condition then
begin
DoSomething;
DoSomethingElse;
end
else
DoADifferentThing;
if Condition then
DoSomething
else
begin
DoADifferentThing;
DoAnotherDifferentThing;
end;
The correct use for your code would be:
procedure InitializeWizard;
begin
Log('Initialize Wizard');
if IsAdminLoggedOn then
begin
SetupUserGroup();
SomeOtherProcedure();
end
else
begin
Log('User is not an administrator.');
msgbox('The current user is not administrator.', mbInformation, MB_OK);
end;
end;
PROGRAM approvedapplicants(input,output);
uses crt;
var
applcntname,housingcomm,clarendon_court,providence_gardens,
sangre_grande_villas:string;
slry,spcslry:integer;
c_qual_sal,s_qual_sal,p_qual_sal,qualifying_salary:integer;
BEGIN
writeln('enter applicant name, salary, spouce salary');
readln(applcntname,slry,spcslry);
writeln('enter housing community');
readln(housingcomm);
BEGIN
qualifying_salary:=0;
IF(housingcomm=clarendon_court)
then
qualifying_salary:=$12500;
writeln('you have selected clarendon court!');
readln(c_qual_sal) ;
end if ;
else if(housingcomm=sangre_grande_villas)then
qualifying_salary:=$9500;
writeln('you have selected sangre grande villas!');
readln(s_qual_sal);
end if ;
else(housingcomm=providence_gardens)then;
qualifying_salary:=$7500;
writeln('you have selected providence gardens!');
readln(p_qual_sal);
end if;
END.
Ordinarily, on SO, we don't post answers to homework/coursework, but your code is so far wide of the mark that I think it's ok to make an exception in this case.
Try compiling and running this program, which I think does pretty much what I think you are intending, then I'll explain a few things about it:
program approvedapplicants(input,output);
uses crt;
var
ApplicantName,
HousingCommunity,
ClarendonCourt,
ProvidenceGardens,
SangreGrandVillas :string;
Salary,
SpouseSalary,
QualifyingSalary : Integer;
CQualSal,
PQualSal,
SQualSal : Integer;
slry,spcslry:integer;
begin
ClarendonCourt := 'Clarendon Court';
ProvidenceGardens := 'Providence Gardens';
SangreGrandVillas := 'Sangre Grand Villas';
QualifyingSalary := 0;
writeln('enter applicant name');
readln(ApplicantName);
writeln('enter salary');
readln(Salary);
writeln('enter spouse salary');
readln(SpouseSalary);
writeln('enter housing community');
readln(HousingCommunity);
if (HousingCommunity = ClarendonCourt) then begin
QualifyingSalary := $12500;
writeln('you have selected clarendon court!');
readln(CQualSal);
end
else
if(HousingCommunity = SangreGrandVillas)then begin
QualifyingSalary := $9500;
writeln('you have selected sangre grande villas!');
readln(SQualSal);
end
else
if HousingCommunity = ProvidenceGardens then begin
QualifyingSalary :=$7500;
writeln('you have selected providence gardens!');
readln(CQualSal);
end;
end.
Firstly, notice how much easier it is to read and follow its logic. This is mainly
because of
The use of a layout (including indented blocks) which reflects the logical
structure of the code.
The use of consistent, lower case for keywords like program, begin, end, etc.
Keywords are usually the least interesting contents of source code, and it is distracting
to have them SHOUTing at you.
The avoidance of arbitrarily dropping characters from variable names (like the "i"
and second "a" of "applicant". In the days of interpreted code running on slow machines there was
argubably some justification for this, but not any more imo. Likewise, the avoidance
of underscores in variable names - admittedly this is more of a personal preference, but
why have you used them everywhere except the applicant's name?
Secondly, you still have quite a bit of work to do.
Having 3 different variables for the salary (?) numbers you prompt the user
for, one for each of the 3 communities, is probably a bad idea unless you will
subsequently want to work with all 3 figures at the same time. Also, you haven't provided text prompts to tell the user what information to enter for the readln(c_qual_sal) etc statements. It wasn't obvious to me what you intend, so I have not tried to guess.
The way you echo the user's choice of community is just creating you a maintenance
headache (what if you want to add more communities later?). It would be better
to have a variable which you set to whichever of the community names matches
what the user has entered.
You have 3 statements to execute for each community, which are duplicated for
each community. The only one you actually need is the QualifyingSalary one -
the others can execute regardless of the inputted community.
I am making simple encrypt/decrypt program in Lazarus with 2 buttons, one for encrypt and one for decrypt. I also have two memo boxes (or just two memos ).
I tested my algorithm and it works but when i tried implementing it in user friendly app i got this problem.
I have this function:
function enc(x:string):string;
var
y:string;
p,q:integer;
m:char;
begin
y:=x[1];
for p:=2 to Length(x)do
begin
q:=p-1;
if chr(ord(x[p]))=' ' then
m:='!'
else if ord(x[p])>ord(x[q]) then
m:=Succ(chr(ord(x[p])))
else
m:=Pred(chr(ord(x[p])));
Y:=y+m ;
end;
enc:=y;
end;
and one procedure to call this function
procedure TForm1.Button1Click(Sender: TObject);
begin
Memo1.Text:=enc(Memo2.Text);
end;
I compiled program and it worked but when i tried to enter some text and encrypt that text i got this error
exception class 'External: SIGSEGV'
In file 'unit1.pas' at line 46: y:=x[1];
I recently started to learn pascal and to use lazarus soo sry if this Q is stupid but i really want to know what I'm doing wrong.
That error, for that code, implies that x is an empty string. If the first character is not valid, then what else could x be, other than empty?
How would i go about creating a procedure that is a thread which continuously passes automatic random generated data within a specified range.
I currently would have to manually enter in each bit of data in the console using this procedure below. I want to creatre a procedure that when running is able to pass data to this procedure as if it was being typed into the console itself.
procedure Analyse_Data is
Data : Integer;
begin
DT_Put_Line("Data input by user");
loop
DT_Get(Data,"Data must be taken as a whole number");
exit when (Data >=0) and (Data <= Maximum_Data_Possible);
DT_Put("Please input a value between 0 and ");
DT_Put(Maximum_Data_Possible);
DT_Put_Line("");
end loop;
Status_System.Data_Measured := Data_Range(Data);
end Analyse_Data;
I havent included the specification files (.ads)
I am new to Ada and any help would be appreciated.
Use an instance of Discrete_Random to generate some number of random data values in the desired range:
subtype Valid_Range is Natural range 0 .. Maximum_Data_Possible;
package Some_Value is new Ada.Numerics.Discrete_Random(Valid_Range);
G : Some_Value.Generator;
…
procedure Generate is
N : Valid_Range;
begin
for I in 1 .. Count loop
N := Some_Value.Random(G);
Put(N);
end loop;
end;
Save the values to a file:
./generate > test_data.txt
Feed that file to your program using I/O redirection from the command line:
./analyse_data < test_data.txt
The exact details will depend on you actual program. See this related Q&A regarding empty lines in standard input.
I developed the following sorting algorithm but there are some run time errors that I cant figure out. The program terminates when it comes to the part of filling the array. I'm still a beginner in ada so I couldn't figure out where the problem is...
With Ada.Text_IO;
With Ada.Integer_Text_IO;
Use Ada.Integer_Text_IO;
Use Ada.Text_IO;
Procedure sort is
n,i,x : Integer;
-- Max_Heapify Function...
Procedure Max_Heapify ( i, n : integer) is
j, Temp : Integer;
begin
Temp:=Int_Acc(i);
j:=2*i;
if Temp>Int_Acc(j) then
elsif Temp<=Int_Acc(j) then
Int_Acc(j/2):=Int_Acc(j);
j:=2*j;
end if;
end loop;
Int_Acc(j/2):=Temp;
end Max_Heapify;
begin
Get(n);
for i in MyArr'range loop
Put_Line("Enter Element " & Integer'Image(i));
Get(MyArr(i));
end loop;
end;
end sort;
Thanks in advance :)
Your Problem is that you are insisting on writing Ada code using c - Style programming paradigms.
Firstly:
The declarations:
Type Arr is array(1..20) of Integer;
Type int_access is access Arr;
MyArr : int_access;
Where you use Int_Acc : in out int_access as parameters to procedures are useless in Ada. You are trying to pass a pointer to an array in (which you are doing!), but you should just pass your Type Arr as in out - The Ada compiler knows to do this as a pointer!
Secondly:
I cannot see where you actually allocate any memory to MyArr. This is a possible source of your runtime error. (when you write to or index an array that does not exist, i would expect to have a problem!)
Thirdly:
You seem to be mixing fixed length arrays with variable length input. If N > 20, you will have a problem.
Fourthly:
Insulting the language is not the best way of getting help from those who like it.
NWS has nailed it : there is a pointer, but no array there.
But it's clear that you have learned C, which leaves you with a lot to learn about other languages including Ada. There really are better ways of doing many things, that aren't taught to C programmers because C doesn't allow them.
Allocating variable sized arrays without pointers, malloc and free for example...
Type Arr is array(positive range <>) of Integer; -- of any size
begin
Put_Line("Enter Number Of Elements Of Array");
Get(n);
declare -- now we know the size
My_Arr : Arr(1 .. n);
begin -- My_Arr is in scope until the end of this block
...
end;
end sort;
Using the type system better...
Bad programming :
for i in 1 .. n loop
Get(MyArr(i));
end loop;
HeapSort(MyArr,n);
for i in 1 .. n loop
Put_Line(Integer'Image(MyArr(i)));
end loop;
This is bad because it violates the DRY principle : loop bounds repeated, and something that hopefully represents the array size passed around as a separate parameter... a maintenance nightmare if you decide to rename n to something meaningful for example.
better programming : Use the type system. Recognise that merely declaring an array has declared a new subtype of integer, representing the index of the array. You can access it as My_Arr'range, and the high bound as My_Arr'last.
for i in My_Arr'range loop
Get(MyArr(i));
end loop;
HeapSort(MyArr);
for i in My_Arr'range loop
Put_Line(Integer'Image(MyArr(i)));
end loop;
And accidents such as redefining n after the array declaration can no longer generate buffer overflows.
NOTE: Heapsort now gets its range from the array. (Max_Heapify may still need a separate parameter to operate on subsets of the array)
Arguably best - if it makes the intent clearer - name the index datatype explicitly and use it...
declare -- now we know the size
subtype My_Range is positive range 1 .. n;
My_Arr : Arr(My_Range);
begin -- My_Arr is in scope until the end of this block
for i in My_Range loop ...
And lastly, which do you prefer; a Storage_Error exception immediately the bug occurs (writing to memory you forgot to allocate) or something odd happening much later because something scribbled across another variable?
EDIT
Having cleared up the major issues two more subtle ones remain...
If I compile the modified program (in Gnat 4.8) I get several warnings : one of them is important and tells you exactly what the problem is...
Most of the warnings stem from the fact that
for i in My_Arr'range loop
declares its own loop variable i which hides any existing in-scope declaration. So you can tidy up the code by removing the unnecessary declarations.
What remains is:
sort.adb:51:28: warning: loop range may be null
sort.adb:51:28: warning: bounds may be wrong way round
The for loop bounds are empty ranges, reversed...
1 .. 3 declares a subtype with 3 values
reverse 1 .. 3 declares the same subtype and iterates backwards over it.
But 3 .. 1 declares an EMPTY subtype (containing NO valid values) so iterating over it - either way round - does precisely nothing.
Hopefully that is the missing part of the puzzle. I'm not clear why one faulty loop gets this warning while the other (at line 38) doesn't...
if j<n **and then** Int_Acc(j+1)>Int_Acc(j) then
j:=j+1;
I think you want just 'and' instead of 'and then,' although I haven't looked at Ada code in years.
Did that compile?