C++ Raiz cuadrada sin librerías

CODE:

#include <iostream>

using namespace std;

int main(){


int num=0;
char ans= 'Y';

do{


cout <<"Square\n Int number: ";

cin >> num;

int i;

for (i = 0; num >= 0; i++) num -= 2*i + 1;

cout << "The Square: " << i-1 <<endl;


cout << "Another time Y/N: \n";
cin >> ans;

}while(ans=='Y'||ans=='y');


return 0;

}