This question already has an answer here:
Lazarus readln doesn't read the variable
(1 answer)
Closed 4 years ago.
I have a small code where I want to initialize an array of records by fields and then just output this records on screen.
Data types:
type
grade = 1..5;
Person = record
Name: string[16];
isMale: boolean;
grades: array [1..6] of grade;
end;
var
Table: array [1..10] of Person;
R: Person;
N,J,I: Integer;
Part of code with initialization and output:
readln(n);
if N>10 then N:=10; if N<1 then N:=1;
for I:=1 to N do begin
R:=Table[I];
//write('Gender?'); readln(j); R.isMale:=j>=0; <= This works just fine
write('Name? '); readln(R.Name);
write('Gender? '); readln(j); R.isMale:=j>=0;
write('Grades? '); for j:=1 to 6 do read(R.grades[J]); writeln;
end;
for I:=1 to N do begin
R:=Table[I];
write(I,' ', R.Name,' ',R.isMale);
end;
When I enter info about first person it works fine, but then every other person's name input is skipped (output is "Name? Gender? ). If I switch entering boolean and string, code works correct, but that's not a logic order.
Why is this happening?
At the end of the loop, you should assign the record to the array. Note that, unlike with classes, assigning a record copies the data in the record, it does not reference the record. So instead of what you have, rather do:
for I := 1 to N do
begin
//write('Gender?'); readln(j); R.isMale:=j>=0; <= This works just fine
write('Name? ');
readln(R.Name);
write('Gender? ');
readln(j);
R.isMale := j >= 0;
write('Grades? ');
for j := 1 to 5 do
read(R.grades[J]);
readln(R.grades[6]); // readln reads the end-of-line too.
writeln;
Table[I] := R; // copy the data from R into the table
end;
That way, the data from the record R is copied into the table. There is no need to copy R from the table at the beginning of the loop, as the table is empty anyway.
Unlike with classes, with records like this, you could do the following too:
write('Name? ');
readln(Table[I].Name);
write('Gender? ');
readln(j);
Table[I].isMale := j >= 0;
// etc...
And in the final loop:
Writeln(I, ' ', Table[I].Name, ' ', Table[I].IsMale);
without using R at all.
Related
I have a problem with Pascal, especially Lazarus.
First of all, I created two random arrays of integer:
procedure TForm1.b_arraycreate1Click(Sender: TObject);
begin
randomize;
for i := 1 to 5 do
arr1[i] := random(10);
end;
And
procedure TForm1.b_arraycreate2Click(Sender: TObject);
begin
randomize;
for j := 1 to 5 do
arr2[j] := random(10);
end;
I know, I could put it in one procedure as well but doesn't matter now.
I want to compare these two. I wrote the following code:
procedure TForm1.b_comparisonClick(Sender: TObject);
var v:boolean;
begin
for i := 1 to 5 do begin
for j := 1 to 5 do begin
if arr1[i] = arr2[j]
then
begin
v:=true;
end
else
begin
v:=false;
end;
end;
end;
if v = true
then
begin
ShowMessage('Yes, there is a similarity! You can find number ' +IntToStr(arr1[i])+ ' in array 1, position ' +IntToStr(i)+ ' and also in array 2, position ' +IntToStr(j)+ '.');
end
else
begin
ShowMessage('No similarities... Generate new ones!');
end
end;
In my own words: I want to push a button and then there should be a message window with the information if there is one number (for example 7) which exists in array 1 and array 2. If yes, it should also write the position (index) of this number.
Unfortunately, this program doesn't work and I don't know why. It always shows "No similarities" (and don't worry about the creation of the arrays. I also have a label where I can test the content of the arrays every time).
Is there a (silly) mistake in my code here?
As explained already by MartynA in his comment, your algorithm is wrong. Your words are:
if there is one number which exists in array 1 and array 2
To see if it is so, you must scan all array1 and, for each number, see if it exists somewhere in array2.
So yes, you need two cycles, one nested in the other. As soon as you find a correspondence, you must stop. Or, if you want more results (find multiple duplicates), show a message instead of stopping - and go ahead. Third possibility (more complicated): when found, store the couple of indexes (without overwrite old results...) and go ahead. I will only show the first option:
procedure TForm1.b_comparisonClick(Sender: TObject);
var
i,j: integer;
v: boolean;
begin
v := false;
for i := 1 to 5 do begin
for j := 1 to 5 do begin
if arr1[i] = arr2[j] then begin
v := true;
break
end
end // inner, j
end; // outer, i
if v = true
then ShowMessage(.....)
else ShowMessage('No similarities...');
end; // proc comparison
I tried to respect your code a bit, there are a few possible "shortcuts"; for example, if v is a boolean variable, it is better to write if v then instead of if v=true then, and some others, like
v := arr1[i]=arr[j];
...or... the outer loop does not need begin+end.
******* BEWARE (see comment below about break)
To stop/exit from two nested cycle is not so simple... perhaps a goto... the code above works, but the break does little work.
******* second update, as described by comment below. IT DOES NOT WORK, because if the break does not exit BOTH loops, the outer index gets modified. The correct cycle using TWO breaks is as follows:
for i := 1 to 5 do begin
for j := 1 to 5 do begin
if arr1[i] = arr2[j] then begin
v := true;
break
end
end; // inner, j
if v then break
end; // outer, i
Sorry for the mistakes... :-)
I would prefer a GOTO to exit both loops: it is faster, single instruction, and more clear ("goto found" instead of a generic break). But GOTOs are not very popular... so I've been afraid!
I have a database and I need to populate it's first 2 columns on every row. The first column is the date and the second column is an id.
My code is as follows:
.......
febr29:array[1..12] of byte = (31,29,31,30,31,30,31,31,30,31,30,31);
.......
procedure TForm.populate_database;
var
i,j,m,n: Integer;
begin
for i := 1 to 12 do
for j := 1 to febr29[i] do
for m := 1 to 9 do
for n := 1 to 15 do begin
database.tbl1.Append;
database.tbl1['date']:= inttostr(j)+'.'+inttostr(i)+'.2016';
database.tbl1['id']:='a'+inttostr(m)+inttostr(n);
database.tbl1.Post;
end;
end;
So basically I need to have all the ids on all the days of the year. But I have a problem with the code above: it gives me some strange output in the database, as in the following picture:
What am I doing wrong?
If your ID field is supposed to identify the data row, it would be better to declare it in the database as an integer column, not a character/string one.
It would also be better & less error prone not to try and calculate it from your loop variables, but use a running counter instead
procedure TForm.populate_database;
var
i,j,m,n: Integer;
ID : Integer;
begin
ID := 0;
for i := 1 to 12 do
for j := 1 to febr29[i] do
for m := 1 to 9 do
for n := 1 to 15 do begin
Inc(ID);
database.tbl1.Append;
database.tbl1['date']:= inttostr(j)+'.'+inttostr(i)+'.2016';
database.tbl1['id'].AsInteger :=ID;
database.tbl1.Post;
Of course, if you must have the 'a' prefix and a character coumn type for some reason, you could do
database.tbl1['id'].AsString :='a' + IntToStr(ID);
but even that may give you results you aren't expecting, unless to pad the result of IntToStr(ID) to a fixed length with leading zeroes.
This is Oracle 11.2g. In a PL/SQL function, I've got a loop whereby each iteration, I create a string and an integer associated with that string. The function returns the final concatenation of all the generated strings, sorted (depending on a function input parameter), either alphabetically or by the value of the integer. To give an idea, I'm generating something like this:
Iteration String Integer
1 Oslo 40
2 Berlin 74
3 Rome 25
4 Paris 10
If the input parameter says to sort alphabetically, the function output should look like this :
Berlin, Oslo, Paris, Rome
Otherwise, we return the concatenated strings sorted by the value of the associated integer:
Paris, Rome, Oslo, Berlin
What is the most appropriate data structure to achieve this sort? I've looked at collections, associative arrays and even varrays. I've been kind of shocked how difficult this seems to be to achieve in Oracle. I saw this question but it doesn't work in my case, as I need to be able to sort by both index and value: How to sort an associative array in PL/SQL? Is there a more appropriate data structure for this scenario, and how would you sort it?
Thanks!
It is very easy if you use PL/SQL as SQL and not like other languages. It is quite specific and sometimes is very nice exactly because of that.
Sometimes I really hate PL/SQL, but this case is absolutely about love.
See how easy it is:
create type it as object (
iter number,
stringval varchar2(100),
intval integer
);
create type t_it as table of it;
declare
t t_it := new t_it();
tmp1 varchar2(32767);
tmp2 varchar2(32767);
begin
t.extend(4);
t(1) := new it(1,'Oslo',40);
t(2) := new it(2,'Berlin',74);
t(3) := new it(3,'Rome',25);
t(4) := new it(4,'Paris',10);
select listagg(stringval,', ') within group (order by stringval),
listagg(stringval,', ') within group (order by intval)
into tmp1, tmp2
from table(t);
dbms_output.put_line(tmp1);
dbms_output.put_line(tmp2);
end;
/
drop type t_it;
drop type it;
Here you can see the problem that you must create global types, and this is what I hate it for. But they say in Oracle 12 it can be done with locally defined types so I am waiting for it :)
The output is:
Berlin, Oslo, Paris, Rome
Paris, Rome, Oslo, Berlin
EDIT
As far as you do not know the amount of iterations from the beginning the only way is to do extend on each iteration (this is only example of extending):
declare
iterator pls_integer := 1;
begin
/* some type of loop*/ loop
t.extend();
-- one way to assign
t(t.last) := new it(1,'Oslo',40);
-- another way is to use some integer iterator
t(iterator) := new it(1,'Oslo',40);
iterator := iterator + 1;
end loop;
end;
I prefer the second way because it is faster (does not calculate .last on each iteration).
This is an example of pure PL/SQL implementation that is based on the idea associative array (aka map or dictionary in other domains) is an ordered collection that is sorted by a key. That is a powerful feature that I have used multiple times. For input data structure in this example I decided to use a nested table of records (aka a list of records).
In this particular case however I'd probably go for similar implementation than in simon's answer.
create or replace package so36 is
-- input data structures
type rec_t is record (
iter number,
str varchar2(20),
int number
);
type rec_list_t is table of rec_t;
function to_str(p_list in rec_list_t, p_sort in varchar2 default 'S')
return varchar2;
end;
/
show errors
create or replace package body so36 is
function to_str(p_list in rec_list_t, p_sort in varchar2 default 'S')
return varchar2 is
v_sep constant varchar2(2) := ', ';
v_ret varchar2(32767);
begin
if p_sort = 'S' then
-- create associative array (map) v_map where key is rec_t.str
-- this means the records are sorted by rec_t.str
declare
type map_t is table of rec_t index by varchar2(20);
v_map map_t;
v_key varchar2(20);
begin
-- populate the map
for i in p_list.first .. p_list.last loop
v_map(p_list(i).str) := p_list(i);
end loop;
v_key := v_map.first;
-- generate output string
while v_key is not null loop
v_ret := v_ret || v_map(v_key).str || v_sep;
v_key := v_map.next(v_key);
end loop;
end;
elsif p_sort = 'I' then
-- this branch is identical except the associative array's key is
-- rec_t.int and thus the records are sorted by rec_t.int
declare
type map_t is table of rec_t index by pls_integer;
v_map map_t;
v_key pls_integer;
begin
for i in p_list.first .. p_list.last loop
v_map(p_list(i).int) := p_list(i);
end loop;
v_key := v_map.first;
while v_key is not null loop
v_ret := v_ret || v_map(v_key).str || v_sep;
v_key := v_map.next(v_key);
end loop;
end;
end if;
return rtrim(v_ret, v_sep);
end;
end;
/
show errors
declare
v_list so36.rec_list_t := so36.rec_list_t();
v_item so36.rec_t;
begin
v_item.iter := 1;
v_item.str := 'Oslo';
v_item.int := 40;
v_list.extend(1);
v_list(v_list.last) := v_item;
v_item.iter := 2;
v_item.str := 'Berlin';
v_item.int := 74;
v_list.extend(1);
v_list(v_list.last) := v_item;
v_item.iter := 3;
v_item.str := 'Rome';
v_item.int := 25;
v_list.extend(1);
v_list(v_list.last) := v_item;
v_item.iter := 4;
v_item.str := 'Paris';
v_item.int := 10;
v_list.extend(1);
v_list(v_list.last) := v_item;
dbms_output.put_line(so36.to_str(v_list));
dbms_output.put_line(so36.to_str(v_list, 'I'));
end;
/
show errors
I need to write a program which demonstrates 2d array, the program need to ask for student name and then the mark.. and this is for 15 students. At the end program outputs 15 names with their marks next to it.
I don't know how to manipulate 2D arrays accurately, I managed to do simple version without using for loop.
`
table: array[1..2, 1..15] of string; {2 rows for 15 columns}
begin
clrscr;
writeln('Enter 15 student names, and a set of marks after each ');
writeln('With marks you can enter more marks after comma for e.g. 34, 26, 31 etc.');
writeln('Enter NAME and SURNAME of STUDENT NR 1 or q to quit ');
read(table[1][1]); {read name in row 1 col 1}
readln;
writeln(' Enter MARKS of STUDENT NR 1 ');
read(table[2][1]); { read mark in row 2 col 1}
readln;
clrscr;
writeln('Enter NAME and SURNAME of STUDENT NR 2 or q to quit ');
read(table[1][2]);
readln;
writeln('Enter MARKS of STUDENT NR 2 ');
read(table[2][2]);
readln; read marks into row 2 column 2}
`
etc. up to student nr 15... but I know I could use two for loops to do that for me instead of copying code for each student... same for output... I've spend many hours to figure out how to do it with different tries... but still Im confused with using two for loops and indexing this array correctly.
could someone help me with this appropriate looping ?
Thanks
Wow, Pascal, haven't seen it for a very long time! It's a good language for learning to program.
Try something like this..
program testarray2d;
uses crt;
var
table: array[1..2, 1..15] of string; {2 rows for 15 columns}
counter: Integer;
Begin
writeln('Enter 15 student names, and a set of marks after each ');
writeln('With marks you can enter more marks after comma for e.g. 34, 26, 31 etc.');
For counter := 1 to 15 do
Begin
writeln('Enter NAME and SURNAME of STUDENT NR ');
write(counter);
write(' or q to quit ');
readln(table[1][counter]);
writeln('Enter MARKS of STUDENT NR ');
write(counter);
readln(table[2][counter]);
clrscr;
End;
End.
Please let me know if it works, because I haven't tested it.
i don't know how to do this:
I want to do a program in pascal in which the user have to insert 90 numbers introduced by console and separated by a blank and keep them in a bidimensional array (10x9). Anyone knows how to implement this?
Thanks a lot.
var the_array:array[1..10] of array[1..9] of integer;
var i:integer; var j:integer;
...
i:=1; j:=1;
while i<=10 do begin
while j<=9 do begin
read(the_array[i,j]);
inc(j);
end;
j:=1;
inc(i);
end;
You just use two indices to iterate through an array while filling it from calling read().
You wrote that you use FreePascal, so you can make use of SScanF here.
This program lets you enter some lines of numbers that are separated by spaces.
After it's done, it prints the numbers.
I would not ever hand something like this over to end users though. Why not provide a graphical user interface instead?
program Project1;
uses
SysUtils;
const
Lines = 10;
type
TNumberArray = array[0..Lines-1,0..9] of integer;
procedure GetNumbers(var nums:TNumberArray);
var Line:Integer; s:String;
begin
for Line := Low(nums) to high(nums) do
begin
Write('Enter line ',Line, ': ');
ReadLn(S);
SScanf(s,'%d %d %d %d %d %d %d %d %d %d',
[
#nums[Line,0],
#nums[Line,1],
#nums[Line,2],
#nums[Line,3],
#nums[Line,4],
#nums[Line,5],
#nums[Line,6],
#nums[Line,7],
#nums[Line,8],
#nums[Line,9]
]
);
end;
end;
procedure ShowNumbers(nums:TNumberArray);
var Line,Col:Integer;
begin
for Line := Low(nums) to high(nums) do
begin
for Col:=Low(nums[Line]) to High(nums[Line]) do
Write(nums[Line,Col], ' ');
WriteLn;
end;
end;
var
Numbers: TNumberArray;
begin
WriteLn('Enter 10 numbers');
GetNumbers(Numbers);
ShowNumbers(Numbers);
WriteLn('Done. Press a key to continue.');
ReadLn;
end.
It's cleaner to parse the line using a TStringList, so that you don't have to hard-code the number of columns, but this should work.