求平方根

#include <iostream>#include <cmath>#include <cstdio>#define E 1e-11using namespace std;int main(){    double a;    cin>>a;    double x0, x1;    x0 = a / 2.0;    while(1)    {        x1 = 0.5 * (a + x0 * x0) / x0;        if(fabs(x1 * x1 - a) <= E)            break;        x0 = x1;    }    //cout << x1 << endl;    printf("%.10f\n", x1);    return 0;}