#include <stdio.h>
#include <math.h>
void main(){
    int i=0,j=0;
    double a[128*1024];
    while (scanf("%lf",&a[i])!=EOF) i++;
    for (j=i-1;j>=0;--j){
        printf("%.4lf\n",sqrt(double(a[j])));
    }
}

Use dynamic variable:
double *a;
a=new double[128*1024]

I can confirm that stack size is 1024k.
To open a bigger array, you need to declare it global instead of in main.

Wasted me 45 mins

Think U!