Високосные года уже не учитывал (найдёте ошибку - не поленитесь написать в комменты)
var a,b,c:integer; begin writeln ('Введите сегодняшний день, месяц, год (например, 1 12 2013)'); read(a,b,c); if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) or ((b=2) and ((a>=1) and (a<=28)) or (((b=4) or (b=6)or (b=9) or (b=11))) and ((a>=1) and (a<=30))) then begin writeln ('Сегодня ',a,'.',b,'.',c); if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) and ((a=31) and (b=12)) then writeln ('Завтра 1.1.',c+1) else if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) and ((a=31) and (b<>12)) then writeln ('Завтра 1.',b+1,'.',c) else if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) and ((a<>31) and (b=12)) then writeln ('Завтра ',a+1,'.',b,'.',c) else if ((b=2) and ((a>=1) and (a<=28))) and ((a=28) and (b=12)) then writeln ('Завтра 1.1.',c+1) else if ((b=2) and ((a>=1) and (a<=28))) and ((a=28) and (b<>12)) then writeln ('Завтра 1.',b+1,'.',c) else if ((b=2) and ((a>=1) and (a<=28))) and ((a<>28) and (b=12)) then writeln ('Завтра ',a+1,'.',b,'.',c) else if (((b=4) or (b=6) or (b=9) or (b=11))) and ((a>=1) and (a<=30)) and ((a=30) and (b=12)) then writeln ('Завтра 1.1.',c+1) else if (((b=4) or (b=6) or (b=9) or (b=11))) and ((a>=1) and (a<=30)) and ((a=30) and (b<>12)) then writeln ('Завтра 1.',b+1,'.',c) else if (((b=4) or (b=6) or (b=9) or (b=11))) and ((a>=1) and (a<=30)) and ((a<>30) and (b=12)) then writeln ('Завтра ',a+1,'.',b,'.',c) else writeln ('Завтра ',a+1,'.',b,'.',c); end else writeln ('Неправильная дата'); end.
var a,b,c:integer;
begin
writeln ('Введите сегодняшний день, месяц, год (например, 1 12 2013)');
read(a,b,c);
if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) or ((b=2) and ((a>=1) and (a<=28)) or (((b=4) or (b=6)or (b=9) or (b=11))) and ((a>=1) and (a<=30))) then
begin
writeln ('Сегодня ',a,'.',b,'.',c);
if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) and ((a=31) and (b=12)) then writeln ('Завтра 1.1.',c+1) else
if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) and ((a=31) and (b<>12)) then writeln ('Завтра 1.',b+1,'.',c) else
if (((b=1) or (b=3)or (b=5) or (b=7) or (b=8) or (b=10) or (b=12)) and ((a>=1) and (a<=31))) and ((a<>31) and (b=12)) then writeln ('Завтра ',a+1,'.',b,'.',c) else
if ((b=2) and ((a>=1) and (a<=28))) and ((a=28) and (b=12)) then writeln ('Завтра 1.1.',c+1) else
if ((b=2) and ((a>=1) and (a<=28))) and ((a=28) and (b<>12)) then writeln ('Завтра 1.',b+1,'.',c) else
if ((b=2) and ((a>=1) and (a<=28))) and ((a<>28) and (b=12)) then writeln ('Завтра ',a+1,'.',b,'.',c) else
if (((b=4) or (b=6) or (b=9) or (b=11))) and ((a>=1) and (a<=30)) and ((a=30) and (b=12)) then writeln ('Завтра 1.1.',c+1) else
if (((b=4) or (b=6) or (b=9) or (b=11))) and ((a>=1) and (a<=30)) and ((a=30) and (b<>12)) then writeln ('Завтра 1.',b+1,'.',c) else
if (((b=4) or (b=6) or (b=9) or (b=11))) and ((a>=1) and (a<=30)) and ((a<>30) and (b=12)) then writeln ('Завтра ',a+1,'.',b,'.',c) else
writeln ('Завтра ',a+1,'.',b,'.',c);
end else
writeln ('Неправильная дата');
end.