Here are some ideas to help you improve your code, and perhaps inspire you to learn more.

## Reconsider `using`
The code currently contains these two lines:

    using std::cout;
    using std::cin;

That's not too terrible, but there are at least two ways to make it better.  First would be to put those *inside* `main` to limit any possible conflicts there instead of globally.  Better, in my view, would be to simply omit them and use `std::cin` and `std::cout` since they're only used in three lines in your entire program.  That way readers will instantly see that you're using the `std::` versions and not some other version.

## Decompose your program into functions
All of the logic here is in `main` in one dense chunk of code.  It would be better to decompose this into a separate function or functions.

## Avoid non-standard features
Other have mentioned this, but declaring and array with anything other than a compile-time number is not in standard C++ and so that should be avoided.  I *hope* your teacher isn't writing C++ code like this!

## Use modern C++ features
It is very likely you haven't learned about `std::ranges` or various other algorithms and data structures yet, but just to whet your appetite, here's a rewrite of your program using C++20 and all of the tools in the toolbox:

```
#include <iostream>
#include <map>
#include <ranges>
#include <algorithm>

int main () {
    using myDataType = float;
    using myMapType = std::map<myDataType, unsigned>;
    myDataType value;
    myMapType counts;
    int N;
    for (std::cin >> N; N && std::cin >> value; --N) {
        ++counts[value];
    }
    auto mode = std::ranges::max_element(counts,{},&myMapType::value_type::second);

    std::cout << "The mode of the data set is " << mode->first 
              << " appearing " << mode->second << " times\n";
}
```