float = (int / int) * 100 ? Doesn't work!

[whitesnow]

I need the answer to be a float because it needs to be a percentage with 2 decimal points of precision. This is for an assignment.

I'm wondering if I can do this without turning them all into floats! Because that causes more problems for me if I do.

This doesn't give me the correct percentage because when the integers divide I lose the precision, it just turns into 0.

Is there any way I can do this with the equation like that?

[lloydchristmas759]

The problem is that the expression on the right-hand side is evaluated using integer arithmetic, and then casted to float when the assignment is done.
The easiest way to fix it is to have the first operand of the right-hand side be a float, so that the whole expression is evaluated using floating point arithmethic:

int a = ...;
int b = ...;
float percent = 100.0f * a / b;

[whitesnow]

Ok thanks a bunch I'll try it out, what is the f next to the 100?

[kbw]

It means 100.0 is a float. If it wasn't there, it would be treated as a double.

[lloydchristmas759]

To make sure it is clear:

100 is an int
100.0 is a double
100.0f is a float

[imi]

Edit: I withdraw this recommendation. Don't do this. ;-)

Just two cents from me: It is absolutely not necessary to write the ".0f " on every place. The compiler will transform constants without any performance loss in the program.

So if it makes the code more readable, this is completely ok:

const float short_PI = 3.1415; // no "f" ending. Doesn't matter.
clearColor(0,0,0,0);  // even if function takes float as parameter, this' work the same 

Ciao, Imi.
PS: Just had to say this, as I think all those surplus .0f make code more unreadable sometimes. ;-)

[Danielsson]

It is absolutely not necessary to write the ".0f " on every place.

Though some compilers display warnings about possible loss of data which could be quite annoying.

[imi]

They do? Even for constants? I had this only when I assign variables to other variables and don't cast them explicitly.

Hm.. bummer.


Ciao, Imi.

[Danielsson]

MS VC++ does. I've just tried it.

[helios]

The compiler will transform constants without any performance loss in the program.

In some cases this can cause inefficient code because the compiler ends up making double to float conversions.
For example, suppose you have:

float a=/*...*/;
a=a*.5;

The compiler always finds the largest type used in an expression and converts all the operands to that type.

[kbw]

It is absolutely not necessary to write the ".0f " on every place

It just so happens that Intel uses the same FPU representation for float/double; but this is not generally true.

If you ignore type conversion warnings, you do so at your peril.

[lloydchristmas759]

It is absolutely not necessary to write the ".0f " on every place.

In the particular case of what whitesnow asked, the ".0" is absolutely necessary, though the "f" isn't. Please don't confuse people...

[imi]

Ok, you convinced me. Thinking twice about it.. I take back my former advice about the ".0f" and replace it with:

In case of doubt, add ".0f" (or ".f" if you're lazy and used to C) when you want a float. Only if you are really sure it won't cause harm, you can consider skip the ".0f". But it's safer and more consistent to just put it there anyway and it's quite easy for things to go wrong..

void clearColor(float r, float g, float b, float alpha) {...} // classic function taking argument from 0-1

// a coder came up with the idea of overloading for the common 0-255 case
void clearColor(int r, int g, int b, int alpha) { clearColor(r/255.f, g/255.f, b/255.f, alpha/255.f); }

...
    // looks pretty. But is just wrong now.
    clearColor(1,1,1,1); // supposed to set to opaque white. 

Ciao, Imi.

[z05DSL3A]

NB: Suffixes are often better in Capitals:

3.1415926f
3.1415926F
3.1415926l
3.1415926L

Edit:
Technically, for a Floating literal (double) all you need to do is put a '.' after the digit sequence e.g. 255. therefor floats can just be '.F' e.g. 255.F

To make sure it is clear:
100 is an int
100.0 and 100. are double
100.0F and 100.F are float
100.0L and 100.L are long double