#include<iostream>
#include<math.h>
using namespace std;
void worc(){
   double k;
   if(cin>>k){
     worc();
     printf("%.4lf\n",sqrt(k));
   }
}
int main()
{
   worc();
   return 0;
}

Your function calls itself very many times.
Write

#pragma comment(linker, "/STACK:10000000")

And you have got 10 mbytes of memory

Thank's