Source code in the xpl0 programming language

include c:\cxpl\codes;                  \intrinsic 'code' declarations


func    WeekDay(Year, Month, Day);      \Return day of week (0=Sat 1=Sun..6=Fri)
int     Year, Month, Day;
[if Month<=2 then [Month:= Month+12;  Year:= Year-1];
return rem((Day + (Month+1)*26/10 + Year + Year/4 + Year/100*6 + Year/400) / 7);
];      \WeekDay


int     MonthTbl, Year, I, C;
[MonthTbl:= [1, 3, 5, 7, 8, 10, 12];            \months with 31 days
C:= 0;
for Year:= 1900 to 2100 do
  for I:= 0 to 6 do                             \for all the 31-day months...
    if WeekDay(Year, MonthTbl(I), 1) = 6 then   \first of month is a Friday
        [C:= C+1;                               \count this year
        if C<=5 or C>201-5 then                 \show first 5 and last 5 years
                [IntOut(0, Year);  ChOut(0, ^ );
                 IntOut(0, MonthTbl(I));  CrLf(0);
                ];
        ];
IntOut(0, C);  CrLf(0);                         \show number of years

\Count and show all years that don't have any 5-weekend months
C:= 0;
for Year:= 1900 to 2100 do
        [for I:= 0 to 6 do                      \for all the 31-day months...
            if WeekDay(Year, MonthTbl(I), 1) = 6 \Friday\ then
                I:= 10;                         \bail out of 'for' loop
        if I<10 then                            \'for' loop completed
                [if (C&$F) = 0 then CrLf(0);    \(format 16 years per line)
                C:= C+1;                        \ without finding a 5-weekend
                IntOut(0, Year);  ChOut(0, ^ ); \ so show the year
                ];
        ];
CrLf(0);  IntOut(0, C);  CrLf(0);               \show number of years
]