Калькулятор на Pascal

For i:=1 to Length(s) do
 if (s[i] in ['0'..'9'])and(not (s[i] in ['*','+','-','/'])) then s1:=s1+s[i] {Собираем первое число}
  else break;
c:=s[i];{запоминаем знак}
For j:=i+1 to Length(s) do
 s2:=s2+s[j] {Собираем второе число}

const
  Operations = ['+', '-', '*', '/'];
  Numbers = ['0'..'9'];
var
  Full_Str, First_Number, Second_Number: String;
  Resul, First_Num, Second_Num, Err: Integer;
  Operation: Char;
  i, j: Byte;
begin
  First_Number:=''; Second_Number:=''; Resul:=0;
  writeln('Введите выражение вида "n+\-\*\/m: ');
  readln(Full_Str);
  for i:=1 to Length(Full_Str) do
    if (Full_Str[i] in Numbers) and not(Full_Str[i] in Operations) then
      First_Number:=First_Number + Full_Str[i]
        else Break;
  Operation:=Full_Str[i];
  for j:=i + 1 to Length(Full_Str) do
    Second_Number:=Second_Number + Full_Str[j];
  Val(First_Number, First_Num, Err);
  Val(Second_Number, Second_Num, Err);
  case Operation of
    '+': Resul:=First_Num + Second_Num;
    '-': Resul:=First_Num - Second_Num;
    '*': Resul:=First_Num * Second_Num;
    '/': Resul:=First_Num div Second_Num;
  end;
  writeln(First_Number, ' ', Operation, ' ', Second_Number, ' = ', Resul);
end.