If Statement when x is near a value

Question

I am trying to solve the numerical equation:

sin^2(x)tan(x) = 0.499999

Using a while loop in C. However I was only able to get program to print an answer if

Answer 1

Use a relative difference, such as:

#include <math.h>

static inline double reldiff(double x, double y)
{
    return fabs(x - y) / fmax(fabs(x), fabs(y));
}

Now your test becomes:

if (reldiff(x, y) < 0.01)   // 1% as requested

Answer 2

Well, a simple solution would be.

if (y >= x-x/100 && y <= x+x/100)
{
   [execute code...]
}

Essentially what it does is check if y is between [x minus 1% of x] and [x plus 1% of x]. Should work alright.