Calculate doubling every 5 years

#include <iostream>
#include <iomanip>

using namespace std;

// You have an investment that doubles
// at the end of every 5 years.
// Write a program that takes amount and years and
// retuns the value of the investment.

const int yrs_to_double = 5; // Doubles at end of 5 years.

// Calculate the final value, given amount and years.
float growth(float amount, float years)
{
    // How many 5-year periods are there?
    int number_of_doublings = years / yrs_to_double;
    float current_doubling = 0; // Each doubling.
    for (int i = 0; i < number_of_doublings; ++i)
    {
        current_doubling = amount * 2; // Double it.
        amount = current_doubling; // Store the doubling.
    }

    return amount; // Return the final amount.
}

int main()
{
    float amount_invested = 0; // Amount to start with.
    int years_to_invest = 0; // Years invested.
    float value_of_investment = 0; // Value after investing.

    cout << "Enter the amount you are investing: ";
    cin >> amount_invested; // Get the starting amount.
    cout << "How many years?: ";
    cin >> years_to_invest; // Get the time to invest.

    // Calculate the value.
    value_of_investment = growth(amount_invested, years_to_invest);

    // Show two decimal points.
    cout << "After investing $" << fixed << setprecision(2)
        << amount_invested << " for " << years_to_invest
        << " years,\nyou now have $" << value_of_investment << ".\n";

    return 0; // End the program.
}