#include<math.h>
#include<iostream>
#include <iomanip>
using namespace std;
#include<cstring>
#include<stdlib.h>

template <class T> class lstack
{
public:
    lstack(int k)
    {
        blink=(T*)malloc(sizeof(T)*k);
        len=k;
        cnt=0;
    }
    ~lstack()
    {
        free(blink);
    }
    T* pop(T* ptr)
    {
        if(cnt==0)
            return NULL;
        cnt--;
        memcpy(ptr,(blink+cnt),sizeof(T));
        return ptr;
    }
    bool push(const T* ptr)
    {
        if(cnt==len)
            return false;
        memcpy((blink+cnt),ptr,sizeof(T));
        cnt++;
        return true;
    }
private:
    T* blink;
    int len,cnt;
};


int main()
{
    lstack<double> s(1000000);//When I use 100000，it's wrong....
    double a;
    while(cin>>a)
    {
        s.push(&a);
    }
    while(s.pop(&a)!=NULL)
    {
        cout<<setprecision(4) <<fixed<<sqrt(a)<<endl;
    }
    return 0;
}

1) We don't need. By task description max input size is 256Kb.
It means max numbers count is 128K.

2) google STL containers - vector, queue, deque, stack.