Comparing floats and doubles in C++

Question

I want to know why the output is different when I'm comparing a float and a double. Only the values are different.
Here's the code:
https://code.sololearn.com/czNb74ZGL18l/#cpp

Answer 1

Hey there ,
Yeh its seems so strange but the thing is computer is still not very good at floating point numbers and uses lot of optimization and rounding for calculations using floating number that's why sometimes these equality operator doesn't work as intended

The exact reason is to do with the *Machine Epsilon*

Machine Epsilon is the smallest number greater than 1.0 that is not equal to 1.0 ( for example if machine Epsilon is 0.1 then you can only have 1.1 , 1.2 or so on you can not have 1.05 or something else) this is machine dependent practically it's very very small

You can check the value of machine Epsilon by this expression

float f;
f = std::numeric_limits<float>::epsilon();

double d;
d = std::numeric_limits<double>::epsilon();

So this is it .
If you want to be exact and be safe
Just use this function instead

// Include iostream and cmath

double epsilon = std::numeric_limits<double>::epsilon()
bool CMP(double a, double b) {
return fabs(a-b) < epsilon ;
}