[Seed7-users] First questions

[Thomas M. <tho...@gm...>]

On Thu, 6 Sep 2012 00:03:09 +0200, Renato Lenzi <re...@gm...> wrote:
> 1) i have to do this simple task: 4 div 3. Ok, i get 1. But what have
> i to do if  i'd like to obtain 1,333333333 instead of 1?

4 and 3 are integer numbers and div is the integer division operator.
For a floating point division you need floating point numbers
and the / division operator. E.g.:

  4.0 / 3.0

If you have integer variables and the division should have a float
result you need to convert the integers to float first. Seed7
does not support implicit type conversions so the the conversion
must be done with the flt function:

  flt(dividend) / flt(divisor)

> 2) why / is ok for floats but if i want to perform a division while
> with integers i have to use "div"? That is why there are different
> operators?

This was inherited from Pascal/Modula/Ada. Additionally it opens the
opportunity to create a rational number with / (see below). Note
that there is another integer division operator mdiv, which acts
different form div:

  div divides and truncates towards 0
  mdiv divides and rounds downward towards minus infinite.

For positive numbers div and mdiv give the same result. The result
just differs when dividend or divisor (or both) are negative.
There are also two remainder operators:

  rem which computes the remainder of a div division.
  mod which computes the modulo, which is the remainder of mod.

The chapter describing the type integer contains tables for the
behavior of 'div', 'rem', 'mdiv' and 'mod':
  http://seed7.sourceforge.net/manual/types.htm#integer

The / operator could be overloaded to work for integers with:

const func integer: (in integer: dividend) / (in integer: divisor) is action "INT_DIV";

In this case 4/3 would return 1. I decided to omit this definition
from the predefined language. Alternatively the / operator could be
overloaded to convert integers to float and to do the division
afterwards:

const func float: (in integer: dividend) / (in integer: divisor) is
  return flt(dividend) / flt(divisor);

In this case 4/3 would return the float value 1.333333333 .
I decided also against this possibility, because it looks like an
implicit conversion.

Instead the / operator, with two integer operands, is used to generate
a rational number. This is defined in the library rational.s7i:
  http://seed7.sourceforge.net/libraries/rational.htm#%28in_integer%29/%28in_integer%29

This way, when rational.s7i is included, the statement

  writeln(4/3 digits 6)

writes

  1.333333

Rational numbers use a 32-bit integer numerator and denominator.
Therefore they are rather limited (integer overflows are not checked).
Alternatively there is the type bigInteger (defined in bigint.s7i),
which allow

  writeln(4_ / 3_ digits 50)

The statement above writes

  1.33333333333333333333333333333333333333333333333333


What do you think about this design decisions?

BTW: I already sent this answer directly to Renato Lenzi.
I just forgot to send it to this group also. So I do it now.

BTW 2: I added an answer to this question to the FAQ.
see: http://seed7.sourceforge.net/faq.htm#div_operator

Regards,
Thomas Mertes