Not precise enough digits

[GonlyG]

I have to use Heron's formula to find a close number to the square root up to (at least!) 7 digits after decimal preciseness. However, even double or long double is not enough. Any suggestions? (I know a vertex has infinite storage size, but surely that wouldn't work..?)

#include <iostream>
using namespace std;
int main() {
    double a, d, val, steps, r;
    cin>>a;
    for (int i=0;i<a;i++){
        r=1; 
        cin>> val>>steps; // To find square root r of a value v, first let r = 1;
       for (int i=0; i<steps;i++)
       {d= val/r; // Calculate d as d = v / r - obviously the better approximation r gives, the closer d will be to it;
        r=(r+d)/2;}       //Calculate average between r and d and use it as the next step approximation, i.e. r{new} = (r + d) / 2);
             cout<<r<<" ";}
}

Output: 17.3781 8.544 302.544 99.3831 6.63325 9.23724 8555 53.5756 21.6564 28.8235 96.1034
Expected: 17.378147197 8.54400374532 302.543827872 99.3830973775 6.63324958071 9.23723724426 8554.99997077 53.5756330375 21.6564078277 28.8235465243 96.1034351588

[sep11]

Have you used setprecision() before?

Maybe that will help. Used in conjunction with "fixed" you should be able to say that you want the double to go to 7 decimal places.

http://www.cplusplus.com/reference/iomanip/setprecision/

[GonlyG]

huzzah! Thanks. :D