Dunno. This is why I asked where you got those values from. 1093.8 obviously isn't 1000*(1+0.09) so that must have been derived by some other calculation.

Just trying an educated guess in a calculator: 1000*(1+0.09/12)^12=1093.806898 -- that seems close; that's the interest rate divided by 12 and applied monthly as compound, thus leading to 9.38% interest rather than the stated 9% -- that may or may not be correct, which is why you need to check where you got 1093.8 from -- who gave you that number, or was it a number you worked out yourself?

Why do you have a variable called monthlyInterestRate? If you're just calculating the value year on year at 9% per annum, you would use the annual rate directly. Or have you been told to calculate the value monthly?

> Well I was just asking if it should look something like that.

No, it'll be very different. You need to declare your variables, and you shouldn't be declaring futureInvestmentValue() as a private function.

> what should go in for the cout part?

Depends what you want to display. If you want to display
1 1093.8
2 1196.41
then probably what you want will be something like:
cout << yearNumber << " " << accumulatedValue << endl;
But you have quite a way to go before that.