Program Pascal Selang hari

hallo, kali ini mimin ingin berbagi tentang program selang hari, tapi program ini belum benar-benar fix yah. kalau ada yang ingin tanya-tanya atau kesulitan mengedit bisa komen atau tanya mimin nanti mimin bantu ^^ makasih! semoga bermanfaat!

program selanghari;
uses wincrt;
var y1, m1, d1, y3, y2, m2, d2, d3, usia1, usia2, r1, r2, i1 , i2, m3, m4 : longint;
begin
     writeln ('Program Selang Hari');
     writeln ('==========================================');
     repeat
       write ('Masukkan tahun I = '); readln (y1);
     until (y1>0);
     repeat
      write ('Masukkan bulan I = '); readln (m1);
     until (m1>0) and (m1<13);
     repeat
       begin
         write ('Masukkan hari  I = '); readln (d1);
         if y1 mod 4 = 0 then
          case m1 of
           1,3,5,7,8,10,12 : usia1 := 31;
           4,6,9,11        : usia1 := 30;
           2               : usia1 := 29;
          end
         else
          case m1 of
           1, 3,5,7,8,10,12  : usia1  := 31;
           4, 6,9,11         : usia1  := 30;
           2                 : usia1  := 28;
          end;
       end;
    until  (d1 >0) and (d1<=usia1);
    i1 := 0;
    m3:=m1;
    if m1 = 1 then r1:= d1
    else
       begin
       for m1:= 1 to m1-1 do
         begin
           if  y1 mod 4 = 0 then
             case m1 of
             1, 3, 5, 7, 8, 10, 12 : usia1 := 31;
             4, 6, 9, 11           : usia1 := 30;
             2                     : usia1 := 29;
             end
             else
            case m1 of
            1, 3, 5, 7, 8, 10, 12 : usia1 := 31;
            4, 6, 9, 11           : usia1 := 30;
            2                     : usia1 := 28;
           end;
          i1 := i1 + usia1;
          end;
        end;
        r1 := i1 + d1;
        writeln;
         repeat
           write ('Masukkan tahun II = '); readln (y2);
        until (y2>0);
     repeat
      write ('Masukkan bulan II = '); readln (m2);
     until (m2>0) and (m2<13);
     repeat
       begin
         write ('Masukkan hari  II = '); readln (d2);
         if y2 mod 4 = 0 then
          case m2 of
           1,3,5,7,8,10,12 : usia2 := 31;
           4,6,9,11        : usia2 := 30;
           2               : usia2 := 29;
          end
          else
          case m2 of
           1, 3,5,7,8,10, 12 : usia2  := 31;
           4, 6, 9,11        : usia2  := 30;
           2                 : usia2  := 28;
          end;
       end;
    until  (d2 >0) and (d2<=usia2);
    i2 := 0;
    m4:=m2;
    if m2 = 1 then r2:= d2
    else
       begin
       for m2 := 1 to m2-1 do
         begin
           if  y2 mod 4 = 0 then
             case m2 of
             1, 3, 5, 7, 8, 10, 12 : usia2 := 31;
             4, 6, 9, 11           : usia2 := 30;
             2                     : usia2 := 29;
             end
             else
            case m2 of
            1, 3, 5, 7, 8, 10, 12 : usia2 := 31;
            4, 6, 9, 11           : usia2 := 30;
            2                     : usia2 := 28;
           end;
          i2 := i2 + usia2;
          end;
        end;
        if y1 mod 4 = 0 then d3:= 366
        else
        d3 := 365;
        y3 := y2-y1;
        r2 := (i2+d2)+(d3*y3);
        writeln;
        begin
         if r1-r2>0 then
         writeln ('Jadi selang hari antara ', d1, '-', m3, '-', y1, ' ', 'dan ', d2, '-', m4, '-', y2, ' ', 'yakni : ', r1-r2)
         else
         writeln ('Jadi selang hari antara ', d1, '-', m3, '-', y1, ' ', 'dan ', d2, '-', m4, '-', y2, ' ', 'yakni : ', r2-r1)
        end;
end.