#include <stdio.h>
#include <time.h>
int main(void)
{
clock_t t = clock();
double d = 0.0;
for (int n = 0; n < 10000; ++n)
for (int m = 0; m < 10000; ++m)
d += d * n * m; printf("Modified a non-volatile variable 100m times. "
"Time used: %.2f seconds\n",
(double)(clock() - t)/CLOCKS_PER_SEC);
t = clock();
volatile double vd = 0.0;
for (int n = 0; n < 10000; ++n)
for (int m = 0; m < 10000; ++m) {
double prod = vd * n * m; vd += prod; }
printf("Modified a volatile variable 100m times. "
"Time used: %.2f seconds\n",
(double)(clock() - t)/CLOCKS_PER_SEC);
}