Calculate Square Root of a Number

#include <iostream>
#include <cmath>
#include <vector>
using namespace std;
// EPSILON is used to denote a small quantity, like an error, 
// or perhaps a term which will be taken to zero in some limit
const double EPSILON = 0.00001;
double SquareRoot(double num) {
	// TODO: Write - Your - Code
	return num;
}

#include <iostream>
#include <cmath>
#include <vector>
using namespace std;
// EPSILON is used to denote a small quantity, like an error, 
// or perhaps a term which will be taken to zero in some limit
const double EPSILON = 0.00001;
double SquareRootRec(double num, double low, double high) {
	double mid = (low + high) / 2;
	double sqr = mid * mid;
	// Finds the difference between the calculated square and given number
	double diff = abs(sqr - num);
	// we can't do a == b for doubles because
	// of rounding errors, so we use error threshold
	// EPSILON. Two doubles a and b are equal if
	//	abs(a-b) <= EPSILON
	if (diff <= EPSILON) {
		return mid;
	}
	// If the square of mid is smaller than num, then in the next recursive call,
	// low will be changed to mid and high remains unchanged.
	if (sqr < num) {
		return SquareRootRec(num, mid, high);
	}
	// Otherwise, that is, if the square of mid is greater than num, then,
	// in the next recursive call, high will be changed to mid and
	// low remains unchanged.
	return SquareRootRec(num, low, mid);
}
double SquareRoot(double num) {
	if (num < 0) {
		return -1;
	} else {
		// Calls recursive function with given number, low and high
		return SquareRootRec(num, 0, 1 + num / 2);
	}
}
int main() {
	vector<double> arr = {-16, 17, 2.25};
	for (int i = 0; i < arr.size(); i++) {
		double ans = SquareRoot(arr[i]);
		string ansStr = (ans == -1) ? " Number is negative." : to_string(ans);
		cout << i + 1 << ". Square root of " << arr[i] << ": " << ansStr << endl;
		cout << "\n-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------\n" << endl;
	}
}