8 олимпиадных задач 1-го семестра, Фадеева ЕП (ПОИТ) / SUBTRACTION06

program subtraction07;
var
n,i,m,l:byte;
a,b,c,d:string;
buf1,buf2,buf,q,del:integer;
k,z:array[1..51] of byte;
begin
readln(a);
n:=length(a);
readln(b);
m:=length(b);
if length(a)>=length(b) then
begin

begin
l:=length(a);
i:=1;
repeat
c[i]:=a[n];
n:=pred(n);
i:=i+1;
until i>length(a);
i:=1;
repeat
d[i]:=b[m];
m:=pred(m);
i:=i+1;
until i>length(b);
i:=1;del:=0;
repeat
val(c[i],buf1,q);
val(d[i],buf2,q);
buf:=buf1-buf2+del;
if buf<0
then begin k[l+1-i]:=buf+10; del:=-1; end
else begin k[l+1-i]:=buf; del:=0; end;
i:=succ(i);
until i>l;
if buf<k[1]
then writeln('Incorrect numbers; try again')
else begin if k[1]=0 then begin for i:=2 to l do write(k[i]);end
else for i:=1 to l do
Write(k[i]); Writeln;

end;
end;
end else Writeln('Incorrect numbers; try again');

end.