Divide two integers resulting into a float

Question

Suppose I want to divide two integer variables and put the result into a float. In order to prevent integer division do I have to program like this:

    int i = 6312;
    int j = 258;
    float f;
    f = i;
    f = i/j;

Or can I straightforward program like below and the compiler makes sure it is handled the 'proper' way:

    f = i/j;

Isn't there a typo in your first block of code? Did you mean to write f = f/j;? Otherwise, (a) why bother assigning f = i;? and (b) the last line of the first block is exactly the same as the line in the second block... So the question doesn't make much sense... unless you made a typo... — Greenonline, Sep 08 '21 at 16:30
@Greenonline: you are correct, in the first block of code I should have written f = f/j; — PimV, Sep 09 '21 at 10:00

score 4 · Accepted Answer · answered Jan 06 '19 at 00:31

4

Cast the integers to float before doing the calculation.

float f = float(i) / float(j);

or

float f = (float) i / (float) j;

Always be clear how the calculation should be done, so the compiler will do what you want it to do.

answered Jan 06 '19 at 00:31

Jot

3,246
1
13
21

3

or float f = (float) i / j; – Juraj Jan 06 '19 at 06:39
@Juraj, that relies on the compiler to do a float calculation when a float and a int are involved. I prefer to make it clear for someone reading the code and for the compiler what is going on without having to think about it. – Jot Jan 06 '19 at 09:12

Greenonline · Answer 2 · 2021-09-09T16:11:08.243

As Arduino is C++, you should really use a static cast, to be technically accurate. However, for Arduino code it probably doesn't really matter.

So either

float f = static_cast< float >(i) / static_cast< float >(j);

or

float f = static_cast< float >(i) / j;

Note: Using a static cast on each operand, rather than just one, is useful to quiet any warnings about the loss of precision with int to float, which typically needs to form a rounded float for large int values.

See C++ int float casting for more info.

Just to add to Jot's answer: Strictly speaking, it should be pointed out that (float) is C, whereas float() is C++.

Also, as you had meant to write in your question:

int i = 6312;
int j = 258;
float f;
f = i;
f = f/j;

Yes, that would work. However, even though it seems quite elegant, it could cause confusion later in time, when someone else examines the code - unless you added a comment explaining why.

it is probably best to keep the code simple and obvious (for debugging purposes) unless you are deliberately intending to obfuscate the code.

Divide two integers resulting into a float

2 Answers2