高精度减法

• const
   max=1000;
  var
  a,b:array[0..max]of longint;
  procedure init;
  var
  s1,s2,s:string;
  l1,l2,i:longint;
  begin
      readln(s1);
      readln(s2);
      l1:=length(s1);
      l2:=length(s2);
      if (l2>l1)or(l1=l2)and(s1<s2) then
      begin
          write('-');
          s:=s1;s1:=s2;s2:=s;
          l1:=length(s1);
          l2:=length(s2);
      end;
      for i:=1 to l1 do
      a[max-l1+i]:=ord(s1[i])-ord('0');
      for i:=1 to l2 do
      b[max-l2+i]:=ord(s2[i])-ord('0');
  end;
  procedure jf;
  var
  g,i:longint;
  begin
      g:=0;
      for i:=max downto 1 do
      if a[i]>=b[i]+g then
      begin
          a[i]:=a[i]-b[i]-g;
          g:=0;
      end else
      begin
          a[i]:=a[i]+10-b[i]-g;
          g:=1;
      end;
  end;
  procedure print;
  var
  i,j:longint;
  begin
      i:=1;
      while (i<max)and(a[i]=0) do inc(i);
      for j:=i to max do
      write(a[j]);
  
  end;
  begin
      init;
      jf;
      print;
  end.