Question

I have this equation

double x = ((newCount/allCount)/.8)*5.0;

newCount is a double with value 0
allCount is a double with value 0

the result of x is -nan(0x8000000000000)

why this happens and how to check this value in objective c to assign default value for it

Answer 1

The problem is that the denominator (allCount) is 0; dividing by zero is not allowed and the answer is not a number. The simplest thing you could do is to test for that before doing the division:

if (allCount != 0) {
  x = ((newCount/allCount)/.8)*5.0
} else {
  x = defaultValue;
}

There are more complicated ways using C’s floating point environment and testing for the FE_DIVBYZERO exception, but while that’s standard it’s rarely used and therefore potentially more difficult for a later reader of the code to comprehend.