求1~1500连续自然数的全部数字之和

编了个程序来解决

var a,b,c,d,i,sum1,sum2,sum3,sum4:longint;
begin
  sum1:=0;
  for i:=1 to 9 do inc(sum1,i);
  writeln(sum1);
  sum2:=0;
  for i:=10 to 99 do begin
    a:=i div 10;
    b:=i mod 10;
    sum2:=sum2+a+b;
  end;
  writeln(sum2);
  sum3:=0;
  for i:=100 to 999 do begin
    a:=i div 100;
    b:=i div 10 mod 10;
    c:=i mod 10;
    sum3:=sum3+a+b+c;
  end;
  writeln(sum3);
  sum4:=0;
  for i:=1000 to 1500 do begin
    a:=i div 1000;
    b:=i div 100 mod 10;
    c:=i div 10 mod 10;
    d:=i mod 10;
    sum4:=sum4+a+b+c+d;
  end;
  writeln(sum4);
  writeln(sum1+sum2+sum3+sum4);
end.