uses crt;
var s1,s2:string;
function cong(x1,x2:string):string;
var tam:string[2];
    du,i,so1,so2,code:byte;
        begin
                cong:='';
                while length(x1)<>length(x2) do
                if length(x1)<length(x2) then insert('0',x1,1)
                else insert('0',x2,1);
                du:=0;
                for i:=length(x1) downto 1 do
                begin
                        val(x1[i],so1);         val(x2[i],so2);
                        so1:=so1+so2+du;
                        du:=0;
                        str(so1,tam);
                        if so1<10 then cong:=tam[1]+cong
                        else
                        begin
                                du:=1;
                                cong:=tam[2]+cong;
                        end;
                end;
                if du=1 then insert('1',cong,1);
                while (cong[1]='0') and (length(cong)>1) do delete(cong,1,1);
        end;

BEGIN
        clrscr;
        write('Nhap so thu nhat:'); readln(s1);
        write('Nhap so thu hai:'); readln(s2);
        write(cong(s1,s2));
        readln
END.

Chúc bạn học tốt!

var s1,s2:string;

function cong(s1,s2:string):string;

var i,nho,so1,so2,kq:byte;

    s:string;

        begin

                cong:='';

                if length(s1)<length(s2) then

                        begin

                        for i:=1 to length(s2)-length(s1) do

                                s1:='0'+s1;

                        end

                else if length(s2)<length(s1) then

                        begin

                        for i:=1 to length(s1)-length(s2) do

                                s2:='0'+s2;

                        end;

                nho:=0;

                for i:=length(s1) downto 1 do

                        begin

                                val(s1[i],so1);

                                val(s2[i],so2);

                                kq:=so1+so2+nho;

                                if kq>=10 then

                                        begin

                                                nho:=1;

                                                kq:=kq mod 10;

                                        end

                                else nho:=0;

                                str(kq,s);

                                cong:=s+cong;

                        end;

                if nho=1 then cong:='1'+cong;

        end;

BEGIN

       clrscr;

       write('Nhap so thu nhat: ');   readln(s1);

       write('Nhap so thu hai: ');   readln(s2);

       write(s1,'+',s2,'= ',cong(s1,s2);

       readln;

end.