C++ I'm a bit stuck on what I did wrong

//Write a program that calculates and prints the final value of a ten year, $10,000
//investment whose annual return gradually declines from 2% to 1% over that term.

#include <iostream>
using namespace std;

double yearlyreturn (double balance, double beginRate, double endRate, int years)
{
        double rateofChange = (beginRate - endRate) / (years - 1);
        balance = balance + balance*rateofChange;
}

double investment (double balance, double beginRate, double endRate, int year)
{
        int years = 0 ;
        while (years <= year)
        {
                yearlyreturn (balance, beginRate, endRate, years);
                years = years + 1;
        }

}


int main() {
  cout << "The return on your investment is ";
  cout << investment(10000, .02, .01, 10);
  // the args cover all the necessary values
}

Thanks in advance!!!