The following code for implementing AVL-tree insertion & deletion gives error #202 (stack overflow).
Source code looks like this:
program Avl_generator; uses Crt;
type p_Avl = ^Avl_node;
Avl_node = record
key: integer;
l, r, par: p_Avl; {pointers to left child, right child, parent}
bal, h: integer {balance factor, height}
end;
procedure init(var root: p_Avl); begin new(root); root:=nil end;
function get_height(var n: p_Avl): integer;
begin
if(n=nil) then get_height:=-1 else get_height:=n^.h;
end;
procedure reheight(var n: p_Avl); {refresh the height variable}
begin
if(n<>nil) then
begin
if(get_height(n^.r)>get_height(n^.l)) then n^.h:=1+get_height(n^.r)
else n^.h:=1+get_height(n^.l);
end;
end;
procedure set_balance(var n: p_Avl); begin reheight(n); n^.bal:=get_height(n^.r)-get_height(n^.l); end; {refresh the balance factor}
function rotate_l(var a: p_Avl): p_Avl; {left rotation, a is pivot}
var b: p_Avl;
begin
b := a^.r;
b^.par := a^.par;
a^.r := b^.l;
if(a^.r<>nil) then a^.r^.par := a;
b^.l := a;
a^.par := b;
if(b^.par<>nil) then
if(b^.par^.r=a) then b^.par^.r := b
else b^.par^.l := b;
set_balance(a); set_balance(b);
rotate_l := b;
end;
function rotate_r(var a: p_Avl): p_Avl; {right rotation, a is pivot}
var b: p_Avl;
begin
b := a^.l;
b^.par := a^.par;
a^.l := b^.r;
if(a^.l<>nil) then a^.l^.par := a;
b^.r := a;
a^.par := b;
if(b^.par<>nil) then
if(b^.par^.r=a) then b^.par^.r := b
else b^.par^.l := b;
set_balance(a); set_balance(b);
rotate_r := b;
end;
function rotate_l_r(var a: p_Avl): p_Avl; {left & right rotation, a is pivot}
begin
a^.l := rotate_l(a^.l);
rotate_l_r := rotate_r(a);
end;
function rotate_r_l(var a: p_Avl): p_Avl; {right & left rotation, a is pivot}
begin
a^.r := rotate_r(a^.r);
rotate_r_l := rotate_l(a);
end;
procedure rebalance(var root: p_Avl; var n: p_Avl); {refresh balance factors and see if sub-trees need rotating}
begin
set_balance(n);
if(n^.bal=-2) then
begin
if(get_height(n^.l^.l)>=get_height(n^.l^.r)) then n:=rotate_r(n)
else n:=rotate_l_r(n);
end
else if(n^.bal=2) then
begin
if(get_height(n^.r^.r)>=get_height(n^.r^.l)) then n:=rotate_l(n)
else n:=rotate_r_l(n);
end;
if(n^.par<>nil) then rebalance(root, n^.par) else root:=n; {recursion here}
end;
procedure insert(var root: p_Avl; what: integer);
var found: boolean;
pre_tmp, tmp: p_Avl;
begin
found:=false; tmp:=root; pre_tmp:= nil;
while(tmp<>nil) and not found do
if(tmp^.key=what) then found:=true
else if(tmp^.key>what) then begin pre_tmp:=tmp; tmp:=tmp^.l end
else begin pre_tmp:=tmp; tmp:=tmp^.r end;
if not found then
begin
new(tmp); tmp^.key:=what;
tmp^.l:=nil; tmp^.r:=nil; tmp^.par:=pre_tmp; tmp^.h:=0; tmp^.bal:=0;
if(pre_tmp=nil) then root:=tmp
else
begin
if(pre_tmp^.key>what) then pre_tmp^.l:=tmp else pre_tmp^.r:=tmp;
rebalance(root, pre_tmp);
end;
end;
end;
procedure delete(var root: p_Avl; what: integer);
var found: boolean;
tmp, pre_tmp, act, pre_act: p_Avl;
begin
found:=false; tmp:=root; pre_tmp:=nil;
while(tmp<>nil) and not found do
begin
if(tmp^.key=what) then found:=true
else if(tmp^.key>what) then
begin pre_tmp:=tmp; tmp:=tmp^.l end
else
begin pre_tmp:=tmp; tmp:=tmp^.r end;
if found then
if(tmp^.l=nil) then
begin
if(pre_tmp=nil) then root:=tmp^.r
else if(pre_tmp^.key>what) then pre_tmp^.l:=tmp^.r
else pre_tmp^.r:=tmp^.r;
dispose(tmp); rebalance(root,pre_tmp);
end else if(tmp^.r=nil) then
begin
if(pre_tmp=nil) then root:=tmp^.l
else if(pre_tmp^.key>what) then pre_tmp^.l:=tmp^.l
else begin pre_tmp^.r:=tmp^.l end;
dispose(tmp); rebalance(root,pre_tmp);
end else
begin
act:=tmp^.l; pre_act:=nil;
while(act^.r<>nil) do begin pre_act:=act; act:=act^.r end;
tmp^.key:=act^.key;
if(pre_act=nil) then begin tmp^.l:=act^.l; dispose(act); rebalance(root,tmp) end
else begin pre_act^.r:=act^.l; dispose(act); rebalance(root,pre_act) end;
end;
end;
end;
var Avl_tree: p_Avl;
begin
init(Avl_tree);
insert(Avl_tree,1);
insert(Avl_tree,2);
insert(Avl_tree,3);
insert(Avl_tree,4);
insert(Avl_tree,5);
writeln(get_path(Avl_tree, 5));
repeat until KeyPressed;
end.
This compiles fine (Turbo Pascal 7.0). When I run the code, though, the error occurs in the rotate_l procedure which is called after the third insertion (whereupon balance factor of the root node =2.
I checked some Java & C++ implementations and the rotation methods there seemed quite similar to mine, therefore I don't know where the problem is..?
Ok, it's been 14 years since I touched Pascal last time :)
So the problem is indeed with rotate_l function.
You are passing a parameter by-reference as indicated by var keyword.
rotate_l(var a: p_Avl)
That causes a to become nil when you overwrite b.par,
Because a references the address of b.par in that particular function invocation and you set b.par to nil.
So a now is referencing memory location that contains nil.
You need to change function signature to pass a parameter by value. This is done by removing var keyword.
rotate_l(a: p_Avl)
Stack overflow is caused by the same issue in rebalance procedure:
Change
procedure rebalance(var root: p_Avl; var n: p_Avl);
to
procedure rebalance(var root: p_Avl; n: p_Avl);
See Free Pascal language reference for parameters
http://wiki.lazarus.freepascal.org/Parameters
Related
So i'm working on this pascal application which has a menu where you can do multiple things.
After entering an album (which is what my program does) and trying to edit it by writing over the current album I get an error as shown in the image.
There have been no errors when compiling except the warning:
(100,9) Warning: Function result variable does not seem to initialized
Here is my code:
program MusicPlayer;
uses TerminalUserInput;
type
// You should have a track record
TrackRec = record
name: String;
location: String;
end;
type TrackArray = array of TrackRec;
GenreType = (Pop, Rap, Rock, Classic);
AlbumRec = Record
name: String;
genre: GenreType;
location: array of TrackRec; // this and track should be track: array of TrackRec
numberOfTracks: Integer;
tracks: TrackArray;
end;
type AlbumArray = array of AlbumRec; // this should be an array of AlbumRec
function ReadGenre(prompt: String): GenreType;
var
option: Integer;
begin
WriteLn('Press 1 for Pop');
WriteLn('Press 2 for Rap');
WriteLn('Press 3 for Rock');
WriteLn('Press 4 for Classic');
option := ReadInteger(prompt);
while (option<1) or (option>3) do
begin
WriteLn('Please enter a number between 1-4');
option := ReadInteger(prompt);
end;
case option of
1: result := Pop;
2: result := Rap;
3: result := Rock;
else
result := Classic;
end;
end;
function CheckLength(prompt: string): Integer;
var
i: Integer;
begin
i := ReadInteger(prompt);
while (i < 0) or (i > 20) do
begin
WriteLn('Please enter a number between 1-20');
i := ReadInteger(prompt);
end;
result := i;
end;
function ReadTracks(count: Integer): TrackArray;
var
i: Integer;
begin
setLength(result, count);
for i := 0 to High(result) do
begin
result[i].name := ReadString('Track Name: ');
result[i].location := ReadString('Track Location: ');
end;
end;
function ReadAlbum(): AlbumRec;
begin
result.name := ReadString('What is the name of the album?');
result.genre := ReadGenre('What is the genre of the album?');
result.numberOfTracks := CheckLength('How many tracks are in the album?');
result.tracks := ReadTracks(result.numberOfTracks);
end;
function ReadAlbums(count: Integer): AlbumArray;
var
i: Integer;
begin
SetLength(result, count);
for i := 0 to High(result) do
begin
result[i] := ReadAlbum();
end;
end;
function ChangeAlbum(count: Integer): AlbumArray;
var
i: Integer;
begin
for i := count to count do
begin
result[i] := ReadAlbum();
end;
end;
procedure PrintAlbum(count: Integer; album: array of AlbumRec);
var
i: Integer;
begin
if count = 1 then
begin
for i := 0 to High(album) do
begin
WriteLn('Album Number: ', i);
WriteLn('Album name is: ', album[i].name);
WriteLn('Album genre is: ', album[i].genre);
end
end;
for i := 1 to count - 1 do
begin
WriteLn('Album name is: ', album[i].name);
WriteLn('Album genre is: ', album[i].genre);
end;
end;
procedure PrintTrack(tracks: TrackArray);
var
i: Integer;
begin
i := ReadInteger('Which track number do you wish to play?');
i := i - 1;
WriteLn('Now playing track: ', tracks[i].name);
WriteLn('Track location: ', tracks[i].location);
end;
function CheckIfFinished(): Boolean;
var answer: String;
begin
WriteLn('Do you want to enter another set of tracks? ');
ReadLn(answer);
LowerCase(answer);
case answer of
'no': result := true;
'n': result := true;
'x': result := true;
else
result := false;
end;
end;
procedure Main();
var
i, count, select, change: Integer;
albums: AlbumArray;
begin
WriteLn('Please select an option: ');
WriteLn('-------------------------');
WriteLn('1. Read Albums');
WriteLn('2. Display Albums');
WriteLn('3. Select an Album');
WriteLn('4. Update an Album');
WriteLn('5. Exit');
WriteLn('-------------------------');
repeat
i := ReadInteger('Your Option:');
case i of
1:
begin
count := ReadInteger('How many albums: ');
albums := ReadAlbums(count);
end;
2:
begin
WriteLn('1. Display All Albums');
WriteLn('2. Display All Albums by Genre');
select := ReadInteger('Your Option: ');
if i = 1 then
begin
PrintAlbum(select, albums);
end;
// if i = 2 then
// WriteLn('1. Pop');
// WriteLn('2. Rap');
// WriteLn('3. Rock');
// WriteLn('4. Classic');
// albums := ReadAlbums(count);
end;
3:
begin
select := ReadInteger('Which album would you like to play? ');
PrintAlbum(select, albums);
PrintTrack(albums[select-1].tracks);
end;
4:
begin
change := ReadInteger('Which album would you like to edit?');
albums := ChangeAlbum(change);
end;
end;
until i = 5;
end;
begin
Main();
end.
The function that the warning refers to, on line 100, is
function ChangeAlbum(count: Integer): AlbumArray;
var
i: Integer;
begin
for i := count to count do
begin
result[i] := ReadAlbum();
end;
end;
The warning says:
Warning: Function result variable does not seem to initialized
And indeed the result variable has not been initialized.
The design of the function is wrong though. You are trying to modify an existing element in an array. You should not be returning a new array. The function is not necessary though. You should simply remove it. Then you need to look at the one place where you call the function.
change := ReadInteger('Which album would you like to edit?');
albums := ChangeAlbum(change);
You should instead code that like this:
change := ReadInteger('Which album would you like to edit?');
albums[change] := ReadAlbum();
I've not checked anything else in your program. I would not be surprised if there are other problems. I've just tried to address the specific question that you asked.
Trying to execute catalan numbers in Pascal but getting fatal syntax error.
Error is :
Fatal: Syntax error, ";" expected but "identifier B" found
Error: /usr/bin/ppcx64 returned an error exitcode
Here is ref code
program main;
var
i,buf: integer;
function catalan(num: integer): integer;
var
sample, returnval : integer;
function bincoeff(n: integer): integer;
var
a,b,retval,numr,denom1,denom2: integer;
bc : integer;
function fact(x: integer): integer;
begin
// fact exec
if x=0 then
fact :=1
else
fact := x* fact(x-1);
end;
begin
//bincoeff exec
a := 2*n
b := n
if a==b then
retval :=1
else if b>a
retval :=0
else
numr := fact(a)
denom1 := fact(b)
denom2 := fact(a-b)
bc := numr /(denom1*denom2)
retval := bc
end;
begin
// catalan exec
sample :=bincoeff(num)
returnval := (sample/(num+1))
end;
begin
for i :=0 to 9 do
begin
buf := catalan(i)
writeln(buf)
end;
end.
Starting with
a := 2*n
till the end of the program you systematically don't use ';'. A fact that, by the way, is signaled pretty clearly by the compiler.
In this context it might be interesting to visit the FreePascal wiki on the topic of the semicolon which points out an important difference between C and Pascal's usage of the semicolon (separator vs terminator). A must-read.
I have to write a program in Pascal which checks whether a word is a palindrome.
For example:
if I input "abba" then write 'TRUE'
input 'abb a' then write 'TRUE'
input 'abca' write 'FALSE'
I wrote this:
program palindromek;
var i,j,delka,pul:integer;
str:string;
function palindrom(slovo:string):boolean;
const mezera=32;
begin
delka:=length(str);
if (delka mod 2) = 0 then pul:=delka div 2
else pul:=(delka-1) div 2;
for i:=1 to delka do
begin
if (ord(slovo[i])>=ord('a')) and (ord(slovo[i])<=ord('z')) then
begin
if (delka>=4)and(delka<=100) then
begin
if (length(str) mod 2) = 0 then {slovo se sudym poctem pismen}
begin
for j:=1 to pul do
begin
if slovo[j]=slovo[length(str)-j+1]
then palindrom:=true else palindrom:=false
end
end else
begin
for j:=1 to pul do
begin
if slovo[j]=slovo[length(str)-j+1]
then palindrom:=true else palindrom:=false
end
end
end else if slovo[1]=slovo[delka]
then palindrom:=true else palindrom:=false
end
end;
end;
begin
readln(str);
writeln(palindrom(str));
end.
but it has to ignore spaces. Do you have any idea please?
To remove all spaces, you can use function like this:
procedure RemoveSpacesInplace(var s: string);
var
i, SpaceCount: Integer;
begin
SpaceCount := 0;
for i := 1 to Length(s) do
if s[i] = ' ' then
Inc(SpaceCount)
else
s[i - SpaceCount] := s[i];
SetLength(s, Length(s) - SpaceCount);
end;
You can modify it for other non-letter chars.
Note that your logic for odd and even length is excessive. Try to simplify it.
You can use the functions StringReplace and ReverseString for your task.
program palindromek;
uses SysUtils, StrUtils;
var
str:string;
function palindrom(slovo:string):boolean;
begin
slovo := StringReplace(slovo, ' ', '', [rfReplaceAll]);
Result := slovo = ReverseString(slovo)
end;
begin
readln(str);
writeln(palindrom(str));
readln;
end.
If you are not allowed to use SysUtils and StrUtils then you can manually reverse your string and then compare if the original string and the reversed string are equal.
This would look something like this: (not tested!)
function palindrom(slovo:string):boolean;
var slovofor: string;
slovorev: string;
i: integer;
begin
for i:= length(slovo) downto 1 do begin
if slovo[i] <> ' ' then begin
slovofor := slovofor + slovo[length(slovo)-i+1];
slovorev := slovorev + slovo[i];
end;
end;
writeln(slovofor);
Result := slovofor = slovorev
end;
Here is an example program from a book. I can't stop the "while not eof" loop. I tried to insert in program "Uses crt;", "const CheckEof: boolean=true" and to press "ctrl+Z" while running, it doesn't work.
Program P123;
uses
crt; {My insertion}
type
Adresacelula = ^Celula;
Celula = record
Info: string;
Urm: AdresaCelula;
end;
var
P, Q, R: AdresaCelula;
s: string;
i: integer;
const
CheckEOF: boolean = true; {My insertion}
Procedure Create;
begin
p := nil;
write ('s='); readln (s);
new (r); r^.Info := s; r^.Urm := nil;
p := r; q := r;
write ('s=');
while not eof do {Here is the loop i need to stop}
begin
readln (s); write ('s=');
new (r); r^.Info := s; r^.Urm := nil;
q^.Urm := r; q := r;
end;
end;
Procedure Display;
begin
r := p;
while r<>nil do
begin
writeln (r^.Info);
r := r^.Urm;
end;
readln;
end;
begin
Create;
Display;
end.
To make the example work, remove the line
const CheckEOF: boolean=true; {My insertion}
and insert CheckEOF:=true; before the Create; call in the main program. Then the program terminates when you press Ctrl-Z.
Your code declares a new variable CheckEOF while you probably want to change CheckEOF of the crt unit.
I have using pascal for my parallel language .(I don't like it , but force.) So the
Merge sort in parallel with fork & join not working, can some one tell me why?
here is my code :
program parrallelmergesort;
architecture shared(100);
const
n=100;(*big array*)
size=10;
var
t,globalCounter:integer;
unsorted:array[1..n] of integer;
procedure CallMerge(var lower,mid,high:integer);
var
i,j,k,count:integer;
S:array[1..n] of integer;
BEGIN
i:=lower;
j:=mid+1;
k:=lower;
count:=high-lower+1;
while (i<=mid) and (j<=high) do
begin
if unsorted[i]<unsorted[j] then
begin
S[k] :=unsorted[i];
i :=i+1;
end
else
begin
S[k] :=unsorted[j];
j :=j+1;
end;
k:=k+1;
end;
if i>mid then
begin
while j<=high do
begin
S[k] :=unsorted[j];
j :=j+1;
k :=k+1;
end;
end
else if j>high then
begin
while i<=mid do
begin
S[k] :=unsorted[i];
i :=i+1;
k :=k+1;
end;
end;
for t:=lower to high do
unsorted[t] :=S[t];
end;
procedure CallMergeSort(bottom,up:integer);
var middle,nextOfMiddle:integer;
begin
if up>bottom then
begin
middle := (up+bottom) div 2;
nextofMiddle :=middle+1;
fork CallMergeSort(bottom,middle);
fork CallMergeSort(nextOfMiddle,up);
join;join;
CallMerge(bottom,middle,up);
end;
end;
begin
unsorted[1] :=4; unsorted[2] :=3; unsorted[3] :=10; unsorted[4] :=5; unsorted[5] :=0;
unsorted[6] :=1; unsorted[7] :=8; unsorted[8] :=6; unsorted[9] :=11; unsorted[10] :=12;
CallMergeSort(1,size);
for globalCounter:=1 to size do
writeln(unsorted[globalCounter]);
readln;
end.
When should I use fork ? before CallMergeSort (Recursive) ?
Last lines is main function in pascal.
don't call fork and join inside the rec function.
Just call them twice from the main.