1)

program tongA;

uses crt;

var n,i: integer;     A: real;

Begin

         clrscr;

         write('nhap n: '); readln(n);

         for i:=1 to n do A:=A+1/(i*(i+2));

         write('A = ',A:2:2);

         readln

End.

2)

program tongB;

uses crt;

var i,B: integer;  

Begin

         clrscr;

         for i:=1 to 100 do

         if i mod 2=0 then B:=B+i;

         write('B = ',B);

         readln

End.

3)

program tongC;

uses crt;

var i: integer;     C: real;

Begin

         clrscr;

         for i:=1 to 50 do C:=C+1/i;

         write('C = ',C:2:2);

         readln

End.

câu lệnh For..Do

uses crt;

var

i,N,B: integer;

A,C: real;

begin

clrscr;

write('nhap so N:=');

for i:=1 to N do

begin

A:=A+1/(i*(i+2);

B:=B+(i*2);

C:=C+1/(i*10);

end;

writeln('kep qua A la ',A);

writeln('kep qua B la ',B);

writeln('kep qua C la ',C);

readln

End.

câu lệnh while..do

uses crt;

var

i,N,B: integer;

A,C: real;

begin

clrscr;

write('nhap so N:=');

while i<=N do

begin

i:=i+1;

A:=A+1/(i*(i+2);

B:=B+(i*2);

C:=C+1/(i*10);

end;

writeln('kep qua A la ',A);

writeln('kep qua B la ',B);

writeln('kep qua C la ',C);

readln

End.