[
easter.tc - tct - 3/18-22/2011 1/14-15/20 4/3/21
http://primepuzzle.com/tc/easter.tc
computes and displays date of Easter given year.
contains an "Easter egg."
]

ceq char s(0),t(0) [
 int i,l;l=strlen(s)
 while ((i<l)*(s(i)==t(i))) i=i+1
 return i==l
 ]

file char f(0) [
 char where(5000);int cnt
 if ((cnt=readfile(f,where,5000))>0) [
   pft where,where+cnt-1
  ]
 ]

init [putchar 34;ps "initially";putchar 34]

main [
 int year,a,b,c,d,e,m,n,of,v(0),cry;cry = 1;char mn(10),an(1),ys(4)
 strcpy mn,"April";strcpy(an,"y")
 pl "";init;ps " written by Daryl D. Gehlbach (ddg)"
 pl "";init;ps " translated from BASIC to tiny-c by Lee R. Bradley (lrb)";pl ""
 pl "This program will compute the date of"
 pl "Easter for any year 1582 to 2099. It"
 pl "is based on a procedure"
 pl "";init;ps " formulated by Carl Friedrich Gauss (cfg)"
 pl "in 1800 at the age of 23.";pl ""
 while ceq(an,"y") [
  pl "What year do you want"
  if cry [putchar 32;init;cry = 0]
  ps " ? ";gs ys
  if ceq(ys,"cfg")+ceq(ys,"lrb")+ceq(ys,"ddg") [file "jgs.txt";abort]
  atoi ys,v;year = v(0)
  while ((year < 1582)+(year > 2099)) [
   pl "";pl "";pl "Year is out of range!"
   pl "Please enter a year from 1582 to 2099."
   pl "What year do you want? ";gs ys
   if ceq(ys,"cfg")+ceq(ys,"lrb")+ceq(ys,"ddg") [file "jgs.txt";abort]
   atoi ys,v;year = v(0)
   ]
  if ((year > 1581) * (year < 1700)) [m = 22;n = 2]
  if ((year > 1699) * (year < 1800)) [m = 23;n = 3]
  if ((year > 1799) * (year < 1900)) [m = 23;n = 4]
  if ((year > 1899) * (year < 2100)) [m = 24;n = 5]
  a = year % 4;b = year % 7;c = year % 19;d = (19 * c + m) % 30
  e = ((2 * a) + (4 * b) + (6 * d) + n) % 7
  of = 9; if ((d + e) <= of) [of = -22;strcpy mn,"March"]
  pl "Easter was / is / will be on ";ps mn;pn d + e - of;ps ",";pn year;ps "."
  pl "Do you wish to try another year (y/n)? ";gs an
  ]
 pl "Thank you, please use me again.";pl "Peace ..."
 ]