Functions Homework Help

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Hello,
I've been attempting this on my own for awhile and I am still drawing a blank.
Here are the instructions listed:
Design an algorithm that will input sales volumes records (until -1) from the user and print the sales commission owed to each salesperson. Input salesperson number, name, and that person's volume of sales for the month. "The commission rate varies according to the sales volume:
sales volume > commission rate
$0.00-$200.00 > 5
$200.01-$1000.00 > 8
$1000.01-$2000.00 > 10
$2000.01 and above > 12

What I have so far, and I know I need other things, any help would be great. I'm not asking anyone to do the work for me, simply lead me in the right directions I will handle the rest.
include <iostream>
using namespace std;
Receive salesVolume();
CalcSalesCommission();
int main()
{
float salesVolume;
float salesCommissions;
float commissionRate;

receive salesVolume(volume)
while(volume != -1)
{
calcCommissionVolume, commissionRate;

I'm stuck here.. I know what I need to do for the other functions and I know there needs to be something to keep track of employee numbers, names, etc, and then print them accordingly. I just can't get past this part and I have a feeling its probably something simple.

Thanks in advance