//en.cppreference.com/w/c/variadic/va_arg.html
#include <stdio.h>
#include <stdarg.h>
#include <math.h>
double stddev(int count, ...)
{
double sum = 0;
double sum_sq = 0;
va_list args;
va_start(args, count);
for (int i = 0; i < count; ++i) {
double num = va_arg(args, double);
sum += num;
sum_sq += num*num;
}
va_end(args);
return sqrt(sum_sq/count - (sum/count)*(sum/count));
}
int main(void)
{
printf("%f\n", stddev(4, 25.0, 27.3, 26.9, 25.7));
}