Giải hệ phương trình tuyến tính( Tú - AT9B)

program baiso3;
uses crt;
type arr=array [1..1000] of real;
var a,b:arr;
    p,n,i,j:integer;
    flag:byte;
    traloi: char;
function doi(x:integer; y:integer) : real;
var k, th:integer;
begin
  th:=0;
  for k:=0 to (x-1) do th:=th+k;
  th:=th+y;
  doi:=a[th];
end;
procedure yeucau;
  begin
  writeln('He phuong Trinh Tuyen Tinh');
  writeln('You Are already');
  write('Yes Or No: (Y/N) '); readln(traloi);
  If traloi in ['y','Y'] then
  begin
  writeln('Nhap he phuong trinh vao de');
  writeln('Any key to continute.......');
  readln;
  end;
  end;
procedure nhap;
var dem:byte;
begin
begin
  yeucau;
end;
  write('nhap so phuong trinh:'); readln(n);
  p:=0;
  for i:=1 to n do
   begin
     dem:=0;
     write('Phuong trinh  ',i , ' : ');
     writeln;
     for j:=1 to i do
       begin
         write('  co he so thu ',j,' = ');
         readln(a[p+j]);
         if a[p+j]=0 then inc(dem);
       end;
     p:=p+i;
     write('  Nhap he so ve phai b[',i,']=');
     readln(b[i]);
     if (a[p]=0) and (b[i]<>0) then flag:=1 ;
     if (dem=i) and (b[i]=0) then flag:=2;
   end;
end;
procedure tinhnghiem;
begin
  b[1]:=b[1]/doi(1,1);
  for i:=2 to n do
  begin
    for j:=1 to i-1 do
      b[i] := b[i]- (doi(i,j)*b[j]);
    b[i]:=b[i]/doi(i,i);
  end;
  write('Nghiem cua he la:');
  for i:=1 to n do
    write(b[i]:0:2,' ');
end;
procedure giaihe;
begin
  if flag=1 then
    write ('He phuong trinh vo nghiem')
  else
    if flag=2 then
      write('He co vo so nghiem')
  else
    tinhnghiem;
end;
begin
  clrscr;
  nhap;
  giaihe;
  readln;
end.