Why my program got "Compilation Error".
if you can help me, i will thank you very much!Thank you.
Here is my grogram:
 const
 way:array[1..31]of string=(' 1',' 2',' 3',' 4',' 5',' 6',' 7',' 8','
9',
                            '10','11','12','13','14','15','16','17','1
8',
                            '19','20','21','22','23','24','25','26','2
7',
                            '28','29','30','31');

var
 a:array[0..6]of string;
 c,day,m,year,days,i,month:integer;

begin
 readln(day,month,year);
 c:=1;fillchar(a,sizeof(a),0);
 a[1]:='mon';a[2]:='tue';a[3]:='wed';a[4]:='thu';
 a[5]:='fri';a[6]:='sat';a[0]:='sun';
 for i:=1 to month-1 do
  case i of
   1,3,5,7,8,10,12: c:=c+31;
   4,6,9,10: c:=c+30;
   2: if ((year mod 4=0)and(year mod 100<>0))or(year mod 400=0) then
c:=c+29 else c:=c+28;
  end;
 days:=trunc((year-1)*(1+1/4-1/100+1/400)+c) mod 7;
 case month of
  1,3,5,7,8,10,12: m:=31;
  4,6,9,10: m:=30;
  2: if ((year mod 4=0)and(year mod 100<>0))or(year mod 400=0) then
m:=29 else m:=28;
 end;
 for i:=1 to days-1 do a[i]:=a[i]+'    ';
 for i:=days to 7 do
  begin
   if i-days+1=day then begin a[i mod 7]:=a[i mod 7]+' ['+way[i-
days+1]+']';Continue;end;
   a[i mod 7]:=a[i mod 7]+'  '+way[i-days+1];
  end;
 for i:=8 to days+m-1 do
  begin
   if i-days+1=day then begin a[i mod 7]:=a[i mod 7]+'  ['+way[i-
days+1]+']';Continue;end;
   if i-days+1=day+7 then begin a[i mod 7]:=a[i mod 7]+'  '+way[i-
days+1];Continue;end;
   a[i mod 7]:=a[i mod 7]+'   '+way[i-days+1];
  end;
 for i:=1 to 7 do writeln(a[i mod 7]);
end.

There are very simle answer for your question:
in CASE operator you using label 10 twice!
Compiler returns 'Dublicate label'