C Source Code/Standard deviation

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
 
#define   NUM_MAX   10
 
/* main: main processing of standard deviation */
/* NOTE: on UNIX you may have to compile with the -lm option 
 * at the *end* of the command line 
 */
int main(void)
{
    int n, i, d, a[NUM_MAX];
    double x = 0, sd, s = 0, m, sum = 0;
 
    printf("enter how many [max %d]: ", NUM_MAX);
    scanf("%d", &n);
 
    if ( n > NUM_MAX )
    {
        printf("You entered a value greater than %d\n", NUM_MAX);
        exit(EXIT_FAILURE);
    }
 
    for (i = 0; i < n; i++)
    {
        printf("enter integer element %d of %d: ", i + 1, n);
        scanf("%d", &a[i]);
    }
 
    for (i = sum = 0; i < n; i++)
    {
        x = x + a[i];
        m = x / n;
        d = a[i] - m;
        sum += d * d;
    }
 
    s = sum / n;
    sd = sqrt(s);
    printf("the number of terms = %d\n", n);
    printf("their mean is m     = %f\n", m);
    printf("standard deviation  = %f\n", sd);
 
    /* indicate success */
    exit(EXIT_SUCCESS);
}