Calculating the interest on a series of loans

I am a college student and started my first week of C++ and we were given an assignment to convert a Java program that calculate the interest on a series of loans given the amount of the principal, the annual interest rate, and the number of days in a sentinel loop into C++.

Here is what we were given:

import java.util.Scanner;
public class ex311
{
public static void main(String[] args)
{
    double principle, rate, interest;
    int days;
    Scanner sc = new Scanner(System.in);
    System.out.print("Enter principle (-1 to end):  ");
    principle = sc.nextDouble();
    while (principle != -1)
    {
        System.out.print("Enter annual interest rate (as a decimal):  ");
        rate = sc.nextDouble();
        System.out.print("Enter number of days:  ");
        days = sc.nextInt();
        interest = principle * rate / 365 * days;
        System.out.printf("Interest is %.2f\n", interest);
        System.out.print("\nEnter principle (-1 to end):  ");
        principle = sc.nextDouble();
    }
}
}

This is what I have for the C++ converted code:

#include 

using namespace std;
void main()
{
    double principle, rate, interest;
int days;
cout > principle;
while (principle != -1)
{
    cout > rate;

    cout > days;

    interest = principle * rate / 365 * days;
    cout > principle;
}
}

I would like to know if there is a better way to go about this, as in making my code more efficient. I am aware that I should not be using void main, but this is how we're being taught for the time being.

-
Do not represent monetary amounts as a decimal type; use an integer type instead.

-
Try to avoid the use of using namespace std.

-
You could still allow the user to enter an interest rate and have the program convert it to a decimal, especially if the user doesn't know how to do this.

-
You could just have days, rate, and interest declared or initialized within the loop. It's usually best to have variables kept in as close scope as possible.

Moreover, if you're going to "list" variables, have each one on a separate line. This is easier to read and avoids the possibility of needing to scroll horizontally.

StackExchange Code Review Q#140448, answer score: 5