#include <vector>

int main()
{
    std::vector<int> v;
    int n;
    while(scanf("%d", &n) != EOF)
    {
        v.push_back(n);
    }

    for(std::vector<int>::reverse_iterator it = v.rbegin(); it != v.rend(); it++)
    {
        printf("%f \n", sqrt((float)(*it)) );
    }

    return 0;
}

You choose %d. It's int. You should use %lf - double!!!