So the nullptr error doesnt show up when i compile it at school and i think i can fix it with adding a line when i compile it, is there another way to get rid of it, and the other two errors i dont understand why im getting them at all. Can someone explain at least the nullptr error?

main.cpp: In function 'int main()':

error: 'array' was not declared in this scope

error: 'hours' was not declared in this scope

error: 'nullptr' was not declared in this scope

```
    int main()
{
    float *studentData;
    int numStudents;
    int size;
    int average = getAverage(*array, *hours);
    int median = getMedian(hours);
    int mode = getMode(hours);

    cout << "How many students were surveyed?  ";
    cin >> numStudents;
    studentData = makeArray(numStudents);

     if (studentData == nullptr)
         cout << "Error allocating memory.";
     else
     {
         getFBData(studentData, numStudents);
         selectionSort(studentData, numStudents);

         for (int i = 0; i < numStudents; i++)
             cout << *(studentData + i) << endl;

         delete[] studentData;
     }

     getAverage(*array, hours);
     printArray(size, hours);
     getMedian(*array, hours);
     getMode(*array, hours);

    cout << "STATISTICS " << endl;
    cout << "\n  Mean: " << average;
    cout << "\n  Median: " << median;
    cout << "\n  Mode: " << mode;

    return 0;
}

```