Use double value as the while loop counter : double « Data Types « C++ Tutorial

1. C++ Tutorial
2. Data Types
3. double

#include <iostream>

using namespace std;

int main()
{  
   double rate = 5;
   double initial_balance = 10000;
   double balance = initial_balance;
   int year = 0;

   while (balance < 2 * initial_balance){  
      balance = balance * (1 + rate / 100);
      year++;
   }

   cout << "The investment doubled after " << year << " years.\n";

   return 0;
}