problem with leap year to count.
lazarus / 62-General

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mikex · 2014-11-21 22:58

Hi there


I have written program for school work 2 times but i cant figure out
the problem. First time my program didn't counted dates like 1.1.2005
- 1.1.2007

Then I fixed that by deleting  small part and rewriting it but now it
dont count the leap year .. i need it exactly from calendar .. 2012 ..
2016.. but its impossible task for me now. I have no time left to try
it and fail gain. 

Commentery and counters are in my language but it does not rly matter
...

Any kind of help with that would be lovely. Thanks.
var d1,d2,m1,m2,r1,r2,i,x,r1i,r2i: integer;     mesic31, mesic30: set
of byte;     dni,dni2: longint;     v:array[1..12] of integer;   begin
write('den1='); readln(d1); write('mesic1=');readln(m1);
write('rok1=');readln(r1); write('den2=');readln(d2);
write('mesic2=');readln(m2); write('rok2=');readln(r2);
mesic31:=[1,3,5,7,8,10,12]; {mesice ktere maji 31 dni}
mesic30:=[4,6,9,11];          {mesice ktere maji 30 dni}  
r1i:=r1;r2i:=r2;       for i:=1 to 12 do begin     if i in mesic31
then     v:=31;     if i in mesic30 then     v:=30;     if i=2 then
     {unor ma 28 dni}     v:=28; end;                     {rozdelime
program do dvou casti: dni a dni2 , dni v rozmezi jednoho roku nebo
vice let} dni:=0; for i:=m1 to 12 do         dni:=dni+v;
        dni:=dni-d1; for i:=m2-1 downto 1 do         dni:=dni+v;
        dni:=dni+d2; r2:=r2-1;   x:=(r2-r1) div 4;
              {jednou za 4 roky pridame jeden den prestupniho roku}
dni:=dni+(365*(r2-r1))+x;   dni2:=0;   for i:=m1 to m2-1 do
         dni2:=dni2+v;          dni2:=dni2-d1+d2; if r1i=r2i then
writeln('pocet dni je ',dni2) else writeln('pocet dni je ',dni);  
readln; end.

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engkin · 2014-11-22 01:14

Number of days in the 2nd month of any year is a function to the year
itself. It seems to me that your code assumes a fixed number: 28 days.
Code: [Select]  for i := 1 to 12 do
  begin
..
    if i = 2 then {unor ma 28 dni}
      v[i] := 28; //<------
  end;

When you use it later in this part:
Code: [Select]  for i := m1 to 12 do
    dni := dni + v[i];
You should consider r1.

While for next part:
Code: [Select]  for i := m2 - 1 downto 1 do
    dni := dni + v[i];
You should consider r2.

This calculation is an approximation, but is not correct for your
purpose.
Code: [Select]  x := (r2 - r1) div 4; {jednou za 4 roky pridame jeden
den prestupniho roku}
  dni := dni + (365 * (r2 - r1)) + x;
For instance, when r1 is a leap year consider the effect of having d1,
m1 prior to the leap day of that year vis. after that day. On the
other hand, not every four years include a leap year.

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Windsurfer · 2014-11-22 09:15

I have not read your code, but a year is a leap year if it is
divisible by 4 unless it is divisible by 100 unless it is divisible by
1000.

Note the second 'unless'. This means that all years divisible by 1000
are NOT leap years. This is a common mistake.

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engkin · 2014-11-22 09:42

Quote from: Windsurfer on November 22, 2014, 10:15:37 amI have not
read your code, but a year is a leap year if it is divisible by 4
unless it is divisible by 100 unless it is divisible by 1000.

Note the second 'unless'. This means that all years divisible by 1000
are NOT leap years. This is a common mistake.
It is 400, not 1000. I know you won't take my word for it  , so here
is Wikipedia:
Quoteif (year is not divisible by 4) then (it is a common year)
else
if (year is not divisible by 100) then (it is a leap year)
else
if (year is not divisible by 400) then (it is a common year)
else (it is a leap year)

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marcov · 2014-11-22 16:58

Dateutils has

Code: [Select]Function IsInLeapYear(const AValue: TDateTime): Boolean;

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engkin · 2014-11-22 18:45

Quote from: marcov on November 22, 2014, 05:58:19 pmDateutils has

Code: [Select]Function IsInLeapYear(const AValue: TDateTime): Boolean;
Can't be used in school assignment.

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Bart · 2014-11-22 22:13

Quote from: engkin on November 22, 2014, 07:45:12 pmQuote from: marcov
on November 22, 2014, 05:58:19 pmDateutils has

Code: [Select]Function IsInLeapYear(const AValue: TDateTime): Boolean;
Can't be used in school assignment.

But function can be copied to impress teacher.

Bart

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BrunoK · 2014-11-23 11:05

Or a different one.
Code: [Select]  function Fun_IsLeapYear(aYear: integer): boolean;
begin
  Result := (aYear and 3) = 0;   // Test simple case
  if Result then begin
    aYear:=aYear shr 2;          // Reduce (Divide by 4)
    Result:=(aYear mod 25)<>0;   // Eliminate those that cannot
    if not Result then           // ..be divided by 100, they are
always leaps
      Result:=(aYear and 3)=0;   // Those that can be divided by 4(00)
are leaps
  end;
end;

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Windsurfer · 2014-11-23 16:42

Engkin,  thanks for the correction.  Thankfully I did know it
correctly in 1999!
The lesson for me is to check before posting.

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engkin · 2014-11-23 23:09

Quote from: Bart on November 22, 2014, 11:13:09 pmBut function can be
copied to impress teacher.
@Bart, your reply cheered me up, thanks. Impressing teachers would
result in harder assignments!

Quote from: Windsurfer on November 23, 2014, 05:42:22 pmThankfully I
did know it correctly in 1999!
@Windsurfer, retaining anything related to this for so long is nearly
impossible for me.