I will do an exam tomorrow, but now I can't run it, can anyone help me?? Thanks!!
program v2
uses
crt;
var
t, dongia: real;
begin
clrscr;
write('nhap t='); readln(t);
if dongia >= 100000 then
t:= 70 / 100 * dongia;
writeln('in don gia:'t);
readln;
end.
Add a semi colon (;) after the program name (so v2;)
Add a comma between the string literal and "t", so ( 'in don gia:',t )
as Roy says in the comments, the logic of your program is wrong. Dongia is uninitialized before the check.
Next time, add a problem description including errormessages and show that you spent some effort/thought in finding the problem.
Put parentheses around the IF condition:
if (dongia>=100000) then
and you should also put a comma in the writeln:
writeln('in don gia:', t);
Related
Recently i just started learn pascal then i found this code
function mengkono(s: integer):integer;
begin
if s < 3 then
mengkono := 3*s+1
else
mengkono := mengkono(s-1) + megnkono(s-2);
end;
begin
writeln(mengkono(6));
readln;
end.
the thing that confused me is this line
else
mengkono := mengkono(s-1) + mengkono(s-2);
from the code above, it's output is 47. Because the input is 6 and 6 is greater than 3 so the line above is ran. Can someone explain to me how it works? i still confused.
This is a recursive function. A function that calls to itself.
If the input is 6 then first it'll do
megnkono:=megnkono(5)+megnkono(4)
then you need to caclulate megnkono(5) and megnkono(4)
for 5 it'll be
megnkono:=megnkono(4)+megnkono(3)
then you need to caclulate megnkono(4) and megnkono(3)
and so on... (pay attention when input is <3 is just giving a direct result)
The function is a recursive function, i.e. it calls itself (the line that confuses you). Every time that line executes, s is slightly smaller and eventually it goes below 3 which stops the recursion.
I think the easiest way of demonstrating the problem is with an example. The code:
PROGRAM CONSTANTSTRING(OUTPUT);
CONST
C_MaxLength = 30;
VAR
small_string : VARYING[5] OF CHAR VALUE 'alpha';
PROCEDURE LocalProc(
localstring : VARYING[C_MaxLength] of CHAR
);
BEGIN
writeln('localstring length: ', localstring.LENGTH);
writeln('localstring size: ', SIZE(localstring.BODY));
writeln('C_MaxLength: ', C_MaxLength);
END;
BEGIN
writeln('small_string length: ', small_string.LENGTH);
writeln('small_string size: ', SIZE(small_string.BODY));
writeln('C_MaxLength: ', C_MaxLength);
LocalProc(small_string);
END.
Compiling:
>pascal /version
HP Pascal I64 V6.1-116 on OpenVMS I64 V8.4
>pascal constantstringinit
>link constantstringinit
>run constantstringinit
And the output:
small_string length: 5
small_string size: 5
C_MaxLength: 30
localstring length: 5
localstring size: 5
C_MaxLength: 5
As you can see the value of C_MaxLength has changed locally inside the LocalProc procedure. Which is odd, since it has been declared a constant.
The new value of the constant is only within the scope of the LocalProc procedure. Code running in main after the call to LocalProc will use the original value of the constant.
At first this looked like a compiler bug to me, but I reasoned that this compiler has been around long enough that something like this would have been detected and either fixed or documented. But, I can't find any documentation on the matter. It doesn't help that VARYING is an HP extension, which means I can't compare to other Pascal implementations.
Do any gurus know more about what's going on here?
It's been a very long time and I can't find documentation to support it, but I think this is a special case of using varying[] of char as the type for a parameter:
localstring : VARYING[C_MaxLength] of CHAR
This not only declares the parameter localstring but also a locally-scoped constant that receives the size of the actual string that's passed in. It's only because you named it the same as your global constant that causes the confusion. You haven't actually changed the value C_MaxLength. Instead you've got another C_MaxLength in the local scope.
Trying changing that line to something like:
localstring : VARYING[foo] of CHAR
and then examine foo as well as C_MaxLength. I expect you'll see foo is 5 and C_MaxLength remains 30.
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'm having a problem when I use these 2 FOR to initialize a two dimensional vector/array:
I have these types defined:
type
Range9 = 0..8;
Digit = '0'..'9';
Board = array [Range9,Range9] of Digit;
and then the part of the code where there are problems with the FOR's is the following:
var
i : Range9;
j : Range9;
table : Board;
BEGIN
for i:=0 to 8 do begin
for j:=0 to 8 do begin
table[i,j] := '0'
end
end;
END.
Now the problem is that, when I debug this portion of code, for some reason, my i variable is modified when it's not supposed to.
For example, I have a watch on i and j and if I put a breakpoint in the line table[i,j] := 0
I see with the watches these values:
i j
0 0
256 1
512 2
768 3
1024 4
1280 5
1536 6
1792 7
2048 8
2049 8
1 0
257 1
513 2
769 3
and so on...
So, when the program enters in the second for (the one that increases the j) my i increases in intervals of 256... I really don't know why is this happening.
And another thing I discovered is that, the problem solves if I change the TYPE of the i variable.
If in the VAR section I put i : integer instead of i : Range9, i doesn't get modified when isn't supposed to.
I would really appreciate if someone explains me why is happening this.
I've found the answer to my own question... well, I didn't exactly found the answer, I've asked this same question in the forum board of the programming course I'm attending and one of the professors gave me this link:
(it's in spanish btw)
http://www.fing.edu.uy/inco/cursos/prog1/pm/field.php/FAQ/Laboratorio#toc17
A quick translation:
This happens with variables defined as subranges. The reason isn't sure; but without doubt is an implementation error of the debugger. There is a 'trick' that can work to solve this (although not always), to be able to see the correct values on the debugger:
Suppose that you have the following variable in your program:
var anything: 1 .. 10;
Add in your program a integer variable which won't be used in any part of the program:
var anything: 1..10;
aux: integer; { only for the debugger }
Then when you define the debugger watch, instead of adding the anything variable, you should add the following expression:
aux:= anything
The aux variable can be used to view different variables, so you only need to declare one aux variable.
In some cases, the previous may not work. Another solution is to change the type of all the variables defined with subranges to integer, char, string, etc (depending the case) only for debug and the change it back again.
end of the translation.
Hope this will be useful for someone else facing the same error.
BTW, this happens with the debugger of free pascal IDE 2.2.2 , maybe in another IDE/compiler/debugger of pascal it doesn't happen.
I haven't done Pascal in a while, so I might be a bit rusty. The only thing I can think of that is creating your problem is that you created a character range that was interpreted as a byte array, which was then converted to a Digits and then multiplied, which gave you those weird values. But, I could be wrong. I am unfamiliar with FreePascal.
Type
Range9 = 0..8
Board = Array[Range9,Range9] of Integer;
var
A : Board;
I,J : Integer;
begin
For I:=0 to 8 do
For J:=0 to 8 do
A[I,J]:=I*J;
end.
Reference: ftp://ftp.freepascal.org/pub/fpc/docs-pdf/ref.pdf
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.)