#include<stdio.h>
#include<stdlib.h>
#include<math.h>
 
int main()
{
   int num = 1;
   char c = 'a';
   float sum = 0, ssum = 0, f = 0;
   char g[8];
   int i = 0,j = 0;
 
   printf("How many numbers to average?");
   i = 0;
   while( i < 7 && (c = getchar()) != '\n') {
        g[i++] = c;
   }
   g[i]='\0';
 
   num = atoi(g);
 
   if(num <= 0) {
      printf("Error must enter value > 1\nExiting...");
      exit(1);
   }
 
   for(j = 0;j<num;++j) {
      printf("Enter number %d of %d:",j+1,num);
      i = 0;
      while( i < 7 && (c = getchar()) != '\n') {
          g[i++] = c;
      }
      g[i]='\0';
      f = atof(g);
      sum += f;
      ssum += f*f;
   }
 
   printf("The standard deviation is %g",sqrt(ssum/num - pow(sum/num,2)));
   getchar();
   return 0;
}