Calculating the sum 1 + x +x^2....

[anzhit]

We have to calculate sum of the terms of a series 1 + x + x^2 ...

..., for a given value of x. x is postive
but less than 1. Write a program to nd the sum by including all those terms, such that the dierence
between the last two terms included in the sum is less than 1.0E-8.
i have written the code it seems to work but it only outputs 6 digits but acc the question i need atlease 9-10 digits whats going wrong ??

#include <iostream>
#include <math.h>

using namespace std;

int main()
{   double x;
    cout << "Enter a number < 1 : " ;
    cin >> x  ;
    double sum = 0 ;
    for(int i =0 ;pow(x,i-1) >= 1.0e-8 + pow(x,i) ;i++)
    {
        sum = sum + pow(x,i) ;
    }
    cout<< sum << endl;
}

[Chervil]

http://www.cplusplus.com/reference/ios/ios_base/precision/
or
http://www.cplusplus.com/reference/iomanip/setprecision/

Your code is pretty direct, but each term is calculated three times. In this case that's maybe not a big deal, though you may like to consider comparing with the saved value of the previous term each time rather than recalculating it.