This program takes n number of element from user (where, n is specified by user), stores data in an array and calculates the average of those numbers.

To understand this example, you should have the knowledge of the following C++ programming topics:

```
#include <iostream>
using namespace std;
int main()
{
int n, i;
float num[100], sum=0.0, average;
cout << "Enter the numbers of data: ";
cin >> n;
while (n > 100 || n <= 0)
{
cout << "Error! number should in range of (1 to 100)." << endl;
cout << "Enter the number again: ";
cin >> n;
}
for(i = 0; i < n; ++i)
{
cout << i + 1 << ". Enter number: ";
cin >> num[i];
sum += num[i];
}
average = sum / n;
cout << "Average = " << average;
return 0;
}
```

**Output**

Enter the numbers of data: 6 1. Enter number: 45.3 2. Enter number: 67.5 3. Enter number: -45.6 4. Enter number: 20.34 5. Enter number: 33 6. Enter number: 45.6 Average = 27.69

This program calculates the average if the number of data are from 1 to 100.

If user enters value of `n` above 100 or below 100 then, while loop is executed which asks user to enter value of `n` until it is between 1 and 100.

When the numbers are entered by the user, subsequently the sum is calculated and stored in the variable `sum`.

After storing all the numbers, `average` is calculated and displayed.