#include <stdio.h>
#include <stdarg.h>
#include <math.h>
double sample_stddev(int count, ...)
{
double sum = 0;
va_list args1;
va_start(args1, count);
va_list args2;
va_copy(args2, args1);
for (int i = 0; i < count; ++i) {
double num = va_arg(args1, double);
sum += num;
}
va_end(args1);
double mean = sum / count;
double sum_sq_diff = 0;
for (int i = 0; i < count; ++i) {
double num = va_arg(args2, double);
sum_sq_diff += (num-mean) * (num-mean);
}
va_end(args2);
return sqrt(sum_sq_diff / count);
}
int main(void)
{
printf("%f\n", sample_stddev(4, 25.0, 27.3, 26.9, 25.7));
}