Is relational comparison between int and float directly possible in C?

Question

I am using Visual Studio 6 with some old time code written in c. I found an issue where the code looks like this..

int x = 3;
float y = 3.0;

if(x == y){
            


        

Answer 1

That's scary. (I wonder what else you'll find.)

x will be promoted to float, but that's not going to help you. Because of how floats are represented, using == to compare them is unreliable.

I might suggest something like this (checking for absolute error/difference) instead:

#define EPSILON 0.0001 
if (fabs((float)x - y) < EPSILON) { /* Do stuff. */ }

which is a common approach and may be sufficient for your purposes, if your values of x and y are "nice". If you really want to go in depth into the topic of comparing floats, this article probably has more information than you want. It does say about the epsilon method:

If the range of the expectedResult is known then checking for absolute error is simple and effective. Just make sure that your absolute error value is larger than the minimum representable difference for the range and type of float you’re dealing with.