```/*
*
*  This file is the solution to an exercise problem posed during
*  one of the UW CSE 333 lectures (333exercises).
*
*  333exercises is free software: you can redistribute it and/or modify
*  the Free Software Foundation, either version 3 of the License, or
*  (at your option) any later version.
*
*  333exercises is distributed in the hope that it will be useful,
*  but WITHOUT ANY WARRANTY; without even the implied warranty of
*  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
*  GNU General Public License for more details.
*
*  You should have received a copy of the GNU General Public License
*  along with 333exercises.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <stdio.h>
#include <stdlib.h>
#include <assert.h>
#include <signal.h>
#include <math.h>

#include "complex.h"

// We use the following global variable to check whether
// a divide-by-zero exception is expected or not.  We'll
// start out not expecting it, and we'll set this to 1 when
// we test a complex division that should trigger a divide by
// zero exception.
static int expect_divzero = 0;

// This is a "signal handler"; in main(), we register this function
// with the operating system using the "sigaction()" system call.
// Do a "man sigaction" to learn about it.
static void handle_divzero(int sig, siginfo_t *si, void *data) {
assert(expect_divzero == 1);
exit(0);  // terminate the process; same as "return 0;" from main
}

// Because floating points are an approximate rather than exact
// representation, you can't directly compare two C doubles and
// expect it to work.  Instead, you need to compare for equality
// within some threshold.  This helper function DoubleEqualsEpsilon
// and EPSILON #define do this.
#define EPSILON ((double) 0.000000000001)
static int DoubleEqualsEpsilon(double a, double b) {
if (a > b) {
// a > b case
if ((a - b) < EPSILON)
return 1;
return 0;
}

// b <= a case
if ((b - a) < EPSILON)
return 1;
return 0;
}

int main(int argc, char **argv) {
Complex a = {1, 2}, b = {3, 4}, c = {0, 0};
Complex res;
struct sigaction act, oldact;

// register our SIGFPE floating point handler
act.sa_flags = SA_RESTART | SA_SIGINFO | SA_ONSTACK;
act.sa_sigaction = &handle_divzero;
assert(sigaction(SIGFPE, &act, &oldact) == 0);

assert(DoubleEqualsEpsilon(res.real, 4.0) == 1);
assert(DoubleEqualsEpsilon(res.imaginary, 6.0) == 1);

res = ComplexSubtract(a, b);
assert(DoubleEqualsEpsilon(res.real, -2.0) == 1);
assert(DoubleEqualsEpsilon(res.imaginary, -2.0) == 1);

res = ComplexMultiply(a, b);
assert(DoubleEqualsEpsilon(res.real, -5) == 1);
assert(DoubleEqualsEpsilon(res.imaginary, 2.0) == 1);

res = ComplexDivide(a, b);
assert(DoubleEqualsEpsilon(res.real, 0.44) == 1);
assert(DoubleEqualsEpsilon(res.imaginary, 0.08) == 1);

// Test the "divide by zero" case.  On modern Intel
// machines and Linux, this causes the returned
// Complex to contain the value "NAN" in both the
// real and imaginary components.  The <math.h>
// function "isnan()" is how we compare to NAN.
// But, to be super paranoid, we've also set up
// a signal handler to catch a SIGFPE floating point
// exception (which integer divide by zero throws).
expect_divzero = 1;
res = ComplexDivide(a, c);
assert(isnan(res.real));
assert(isnan(res.imaginary));

return 0;
}
```