PASCAL中组合数怎么求

用函数或用过程都可以求

var
a:array[1..1000]of integer;
i,j,n,r:integer;
begin
readln(n,r);
a[1]:=n;
i:=1;
repeat
if a[i]>r-i then
if i=r then
begin
for j:=1 to r do write(a[j]);
writeln;
dec(a[i]);
end
else
begin
a[i+1]:=a[i]-1;
inc(i);
end
else
begin
dec(i);dec(a[i]);
end
until a[1]=r-1;
end.