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

int main(int argc, char **argv)
{
    FILE *fp;
    double x=0.0, mean=0.0, s1=0.0, ss=0.0, n=0.0;

    if ( argc != 2 ) {
        printf("### You need a file name.\n");
        exit (EXIT_FAILURE);
    }
    if ( (fp = fopen(argv[1],"r")) == NULL )  {
        printf("### Could not open a file [%s].\n",argv[1]);
        exit (EXIT_FAILURE);
    }
    while ( fscanf(fp, "%lf", &x) != EOF) {
        n += 1.0;
        s1 = x - mean;
        mean += s1 / n;
        ss += (n-1.0)/ n * s1 * s1;
    }
    fclose(fp);

    printf("n=%d, mean=%f, variance=%f, s.d.=%f\n",
           (int)n, mean, ss/n, sqrt(ss/n));

    return EXIT_SUCCESS;
}