(C++）使用while循环计算平均数

需要一些帮助，了解如何使用计数器、累加器和结束哨兵（基本编程hwk，耶！）来查找儿童出售的饼干的平均盒数。我在弄清楚为什么averageBoxes打印出错误的数字时遇到了问题。

例如：

程序结果打印出-5个平均框，当这显然不正确时。。。

{
    int numBoxes,
        // Number of boxes of cookies sold by one child
        totalBoxes = 0,   // Accumulates total boxes sold by the entire troop
        numSeller = 1;    // Counts the number of children selling cookies
    double averageBoxes; // Average number of boxes sold per child
                         // Write code to initialize the totalBoxes accumulator to O and
                         // The numSeller counter to 1.
    cout << "**** Cookie Sales Information ****n";
    // Get the first input
    cout << "Enter number of boxes of cookies sold by seller " << numSeller
        << " (or -1 to quit): ";
    cin >> numBoxes;
    // Write code to start a while loop that loops while numBoxes
    // is not equal to -1, the sentinel value.
    while(numBoxes != -1)
    {
        // Write code to add numBoxes to the totalBoxes accumlator.
        // Write code to add 1 to the numSeller counter.
        totalBoxes += numBoxes;
        numSeller++;
        // Write code to prompt for and input the number of boxes
        // sold by the next seller.
        cout << "Enter the number of boxes sold by girl scout # " << numSeller << ": ";
        cin >> numBoxes;
    }
    // When the loop is exited, the value stored in the numSeller counter
    // will be one more than the actual number of sellers. So write code
    // to adjust it to the actual number of sellers.
    numSeller = numSeller - 1;
    if(numSeller == 0)       // If true, -1 was the very first entry
        cout << "nNo boxes were sold.n";
    else
    {  // Write code to assign averageBoxes the computed average number
       // of boxes sold per seller.
       // Write code to print out the number of sellers and average number
       // of boxes sold per seller.
        averageBoxes += numSeller / numBoxes;
        cout << "The average number of boxes sold by the " << numSeller << " sellers was " << averageBoxes << endl;
    }
    return 0;
}

这可能是一个简单的解决方案，但任何帮助都将不胜感激，谢谢！