Ghi tích 2 ma trận ra file

uses crt;
type mang=array[1..10,1..10] of byte;
var
  f:text;
  a,b,c: mang;
  n: byte;
procedure nhap(var m:mang; ch: char);
var i,j:byte;
begin
  writeln('Nhap ma tran ',ch);
  for i:=1 to n do
    for j:=1 to n do
      begin
        write('  ',ch,'[',i,',',j,']= ');
        readln(m[i,j]);
      end;
end;
procedure xuat(m: mang; ch: char);
var i,j:byte;
begin
  writeln('Xuat ma tran ',ch);
  for i:=1 to n do
    begin
      for j:=1 to n do write(m[i,j]:3);
      writeln;
    end;
end;
procedure nhan;
var
  i,j,k:byte;
  f: text;
begin
  for i:=1 to n do
    for j:=1 to n do
      begin
        c[i,j]:=0;
        for k:=1 to n do c[i,j]:=c[i,j]+a[i,k]*b[k,j];
      end;
end;
procedure ghimatran(m:mang;ch:char);
var i,j: byte;
begin
  writeln(f,'Ma tran ',ch);
  for i:=1 to n do
    begin
      for j:=1 to n do  write(f,m[i,j]:3);
      writeln(f);
    end;
end;
begin
  clrscr;
  write('Nhap n= '); readln(n);
  nhap(a,'a');
  nhap(b,'b');
  nhan;
  xuat(a,'a');
  xuat(b,'b');
  xuat(c,'c');
  {Ghi file}
  assign(f, 'matran.txt');
  rewrite(f);
  writeln(f,n);
  ghimatran(a,'a');
  ghimatran(b,'b');
  ghimatran(c,'c');
  close(f);
  readln;
end.