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***drdebcol*** · 07-19-2009, 06:17 PM

This is an interesting algorithm. I used mathematical formula for calculating day in week if you know date ! If someone wants to know mathematical formula, just PM me !

Code:

program day_in_week;

uses wincrt;

var

day,month,year:integer;

s:string;

function numcheck(s:string):boolean;

 var

  x:integer;

  begin

   numcheck:=true;

    for x:=1 to length(s) do

     if (ord(s[x])<48) or (ord(s[x])>57) then

      if s[x]<>'' then

       numcheck:=false;

  end;

function strtoint(s:string):integer;

 var

   check:integer;

   i:integer;

  begin

   if numcheck(s) then

    val(s,i,check);

     strtoint := i;

end;

function week_day(n:integer):string;

 var

   k:array[0..6] of string;

begin

  k[0]:='Sunday';

  k[1]:='Monday';

  k[2]:='Thursday';

  k[3]:='Wednesday';

  k[4]:='Tuesday';

  k[5]:='Friday';

  k[6]:='Saturday';

  week_day:=k[n];

end;

function week(d,m,y:integer):integer;

 var

   g,v,main:integer;

begin

   g:=y mod 100;

   v:=y div 100;

   m:=m-2;

   if m=-1 then

     begin

       m:=11;

       g:=g-1;

     end;

   if m=0 then

     begin

       m:=12;

       g:=g-1;

     end;

  main:=(d+trunc(2.6*m-0.2)-2*v+g+trunc(g/4)+trunc(v/4)) mod 7;

  week:=main;

end;

begin

writeln('Enter date ! (dd.mm.yyyy)');

readln(s);

day:=strtoint(copy(s,1,pos('.',s)-1));

s:=copy(s,pos('.',s)+1,length(s));

month:=strtoint(copy(s,1,pos('.',s)-1));

s:=copy(s,pos('.',s)+1,length(s));

year:=strtoint(s);

writeln(week_day(week(day,month,year)));

end.

***l3g1sl4tor*** · 07-24-2009, 08:20 AM

Interesting program! Smile

I tried to form formula by myself and got some on factorials base... Is it true?! Smile

***drdebcol*** · 07-24-2009, 08:11 PM

Well formula is not with factorials, but it is a bit complicated !
Here is the formula :

Code:

D=( d + [2.6*m + 0.2] - 2*v + g + [g/4] + [v/4] ) (mod 7)

So here is the explanation of this formula :

Code:

D - Day in week that you want to get 

(0=Sunday, 1=Monday . . .6=Saturday)

m - month (1=March, 2=April . . . 10=December,11=January,12=February)

As you can see January and February are like months of year before !

g - years (for 1995 year is 95, except for January and February where year is 94 so g=94)

(mod 7) - Rest after division with 7 ! (you know mod in Pascal)

d - Day in month (1..31)

[x] - the biggest integer number that is not bigger than x (trunc() function in Pascal !)

v - number of centuries (for 1995 number of centuries is 19 so v=19)

I hope you understand, if you don't understand, just ask !
BTW This is formula from book "Matematičke Formule" or "Mathematical Formulas" author : Dragoslav Herceg place : Novi Sad

***l3g1sl4tor*** · 07-25-2009, 06:40 AM

lol... what a crazy mathematic guy is that Dragoslav... Interesting aspect of thinking! Smile

I just dont understand part [2.6*m + 0.2] but nwm... i must to work hard in area of mathematic to realize solution... dont tell me it! Smile