Câu 1:

uses crt;
var f:text; a,b:longint;
begin
clrscr;
   write('Nhap so thu nhat: ');readln(a);
   write('Nhap so thu hai: ');readln(b);
   writeln('Hieu = ',a-b);
   assign(f,'hieunguyen.cpp');rewrite(f);
      writeln(f,'Hieu = ',a-b);
   close(f); 
readln
end.

Câu 2: 

uses crt;
var f:text; a,b:longint;
begin
clrscr;
   write('Nhap chieu dai: ');readln(a);
   write('Nhap chieu rong: ');readln(b);
   writeln('Dien tich = ',a*b);
   assign(f,'dientichhcn.cpp');rewrite(f);
      writeln(f,'Dien tich = ',a*b);
   close(f); 
readln
end.

Câu 3:

uses crt;
var f:text; i,s:longint;
begin
clrscr;
   assign(f,'tongdv5.cpp');rewrite(f);
      for i:=0 to 100 Do 
         if i mod 10=5 then s:=s+i;
      writeln(f,'Tong = ',s);
   close(f); 
readln
end.

Câu 1:

uses crt;
var f:text;
   a,b:longint;
begin
   clrscr;
   write('Nhap hai so: '); readln(a,b);
   write('Hieu hai so vua nhap: ',a-b);
   assign(f,'hieunguyen.cpp'); rewrite(f);
   write(f,'Hieu hai so vua nhap: ',a-b);
   close(f);
   readln;
end.

Câu 2:

uses crt;
var f:text;
   a,b:longint;
begin
   clrscr;
   write('Nhap chieu dai, chieu rong: '); readln(a,b);
   write('Dien tich HCN: ',a*b);
   assign(f,'dientichhcn.cpp'); rewrite(f);
   write(f,'Dien tich HCN: ',a*b);
   close(f);
   readln;
end.

Câu 3:

uses crt;
var f:text;
   s,i:longint;
begin
   clrscr;
   s:=0;
   for i:=0 to 100 do if i mod 10=5 then inc(s,i);
   write('Tong: ',s);
   assign(f,'tongdv5.cpp'); rewrite(f);
   write(f,'Tong: ',s);
   close(f);
   readln;
end.