Source code in the freebasic programming language

dim shared as ubyte fdoom(0 to 1, 1 to 12) = {_
    { 3, 7, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5 }, _
    { 4, 1, 7, 4, 2, 6, 4, 1, 5, 3, 7, 5 } } 'the first doomsday in
                                             'each month for common
                                             'and leap years

dim shared as string*10 days(0 to 6) = {"Sunday", "Monday", "Tuesday", "Wednesday",_
                              "Thursday", "Friday", "Saturday"}

function doomsday(y as uinteger) as ubyte
    ' John Conway's doomsday formula
    return (2 + 5*(y mod 4) + 4*(y mod 100) + 6*(y mod 400)) mod 7
end function 

function leap(y as uinteger) as ubyte
    'is it a leap year? 
    'return 0 for common years, 1 for leap years
    if y mod 4 > 0 then return 0
    if y mod 100 = 0 and y mod 400 > 0 then return 0
    return 1
end function

function get_day(y as uinteger, m as ubyte, d as ubyte) as string
    dim as ubyte c = doomsday(y), diff
    diff = (7 + d - fdoom( leap(y), m )) mod 7
    return days( (c+diff) mod 7 )
end function

print get_day( 1800, 01, 06 )
print get_day( 1875, 03, 29 )
print get_day( 1915, 12, 07 )
print get_day( 1970, 12, 23 )
print get_day( 2043, 05, 14 )
print get_day( 2077, 02, 12 )
print get_day( 2101, 04, 02 )