#include "stdio.h"
#include "math.h"
int main()
{
    float a[32768];
    int i,j=0;
    while(scanf("%f",&a[j])!=EOF)j++;
    for(i=0;i<=j;i++)printf("%.4f\n",sqrt(a[i]));
    return 0;
}
Why??How could I stop it?

The first: don't use float - need double (you lost precision)
The second: amount of numbers in input can be at most 128*1024 (it is more than 32768)