What is the best technique for checking whether a floating point or double value is the same as exactly zero?

Question

What will be an ideal response?

Answer 1

Due to the way floating point and double values are stored, it is not possible to perform accurate checking with the same as operator. The best technique to use for checking whether a floating point value is the same as zero (or any other value) is to obtain the absolute value of the difference of the number and what we are checking for, such as zero. If the difference is very small, such as 0.00001, we may assume the value is zero (or very close). For example, to check if the value of the variable “x” is zero, the check could be performed as shown here:
```
double x;
// set the value in x
if( fabs(x – 0.0) < 0.00001) // checking to see if x is 0.0
{
// assume x is 0.0
}

double y;
// set the value in y
if( fabs(y – 25.0) < 0.00001) // checking to see if y is 25.0
{
// assume y is 25.0
}
```