integer division

Question

By definition the integer division returns the quotient.

Why 4613.9145 div 100. gives an error ("bad argument") ?

Answer 1

For div the arguments need to be integers. / accepts arbitrary numbers as arguments, especially floats. So for your example, the following would work:

1> 4613.9145 / 100.  
46.139145

To contrast the difference, try:

2> 10 / 10.
1.0

3> 10 div 10.
1

Documentation: http://www.erlang.org/doc/reference_manual/expressions.html

---

Update: Integer division, sometimes denoted \, can be defined as:

a \ b = floor(a / b)

So you'll need a floor function, which isn't in the standard lib.

% intdiv.erl
-module(intdiv).
-export([floor/1, idiv/2]).

floor(X) when X < 0 ->
    T = trunc(X),
    case X - T == 0 of
        true -> T;
        false -> T - 1
    end;

floor(X) -> 
    trunc(X) .

idiv(A, B) ->
    floor(A / B) .

Usage:

$ erl
...
Eshell V5.7.5  (abort with ^G)
> c(intdiv).
{ok,intdiv}
> intdiv:idiv(4613.9145, 100).
46

Answer 2

Integer division in Erlang, div, is defined to take two integers as input and return an integer. The link you give in an earlier comment, http://mathworld.wolfram.com/IntegerDivision.html, only uses integers in its examples so is not really useful in this discussion. Using trunc and round will allow you use any arguments you wish.