Visual Studio forgot how to do math?

[Polorboy]

So I am using Visual Studio 2012 Professional, this is C++ code. I am just trying to get the remainder from a very simple division. Nothing difficult, heres the code:

double getProbability(){
		int rd = random();
		int max = numeric_limits<int>::max();
		double result = rd % max;
		cout << "Probability: " << result << "\n";		
		return result;
	}

When I look at the values in debug I get:

max     2147483647
rd      1804289383
result  1804289383.0000000

Umm.... that is completely wrong. The answer should be 0.840188. What is going on here?

random() just returns a number from a vector that was prepopulated with "random" integers. Not really random, but that isn't all that important. What is important is why on earth is a % operation returning such a huge number. I assigned the values to variables so I could look at them in the debugger. I know I am going to probably get a thousand different ways that I could do this "better" but again, that isn't what I am looking for. I would just like someone to explain to me why the % operation is doing what it is doing?

[naraku9333]

The modulus is doing exactly what it is supposed to do. You probably want division, but you will need to cast either rd or max to double.

[Polorboy]

So, when did % change from giving a remainder to doing what ever it is that is doing there? My understanding, and the way I have been using / and % for years is that / will give everything to the left of a decimal point, and % returns everything to the right of the decimal point, the remainder? I am honestly confused, I am not trying t be facetious or anything like that. This is honestly the first time I have ever seen a result like that from using %.

[o1vk4iN6]

Polorboy forgot how to do math?

Always find it funny when someone blames the tools.

[Polorboy]

Polorboy forgot how to do math?


Always find it funny when someone blames the tools.

And I always find it funny when someone trolls.

[firedraco]

double result = rd % max;

>_>

[Polorboy]

Just realized what was going on, this is what happens when you code on little sleep. The little things get you. The number is right, I just want the decimal at the other end of the number.

[naraku9333]

@Polorboy
I don't think you understand how modulus works http://www.cprogramming.com/tutorial/modulus.html
Modulus returns the remainder of integer division but if the numerator is smaller it is returned.

[Disch]

+1 @ naraku.

Modulus does nothing regarding the "decimal point". What it does it it gives you the remainder after a division (read: integer remainder).

So... 7 % 3 == 1 , because 7 / 3 is 2 remainder 1.

If you are doing x % max, then odds are very high you're going to just get x, unless x == max (in which case you'd get 0).

[TheIdeasMan]

@Polorboy

Maybe these were what you are after.

http://www.cplusplus.com/reference/cmath/fmod/

and std::modf

Btw xerzi is right, don't blame the tools in the first instance - you wouldn't say that your calculator can't do math would you?

Hope all goes well.