C++ 2D array function

Question

Basically I have,

    double marks [STUDENTS][ASSIGNMENTS] = {    (0.1,0.2,0.3,0.4,0.5,0.6,0.7),
                                            (1,0.9,0.8,0.7,0.6,0.5,0.5),
                                            (0.8,0.8,0.8,0.8,0.8,0.8,0.8),
                                            (0.8,0.9,0.7,0.8,0.9,0.7,0.8),
                                            (0.5,0.6,0.7,0.8,0.9,0.5,0.9)};

And I want to get: double studentAverages [STUDENTS] from studentAverages=calculateStudentAverages(marks);

Using:

    double calculateStudentAverages (double marks[STUDENTS][ASSIGNMENTS]){
    double averages[STUDENTS];
    double average;
    for (int i = 0; i < STUDENTS; i++) {
            for (int j = 0; j < ASSIGNMENTS; j++) {
                average = average + marks[i][j];

            }
            averages[i]=average/ASSIGNMENTS;

    }    
    return averages;
}

But I get "cannot convert from 'double [5]' to 'double'" and "cannot convert from 'double' to 'double [5]'"

You should avoid raw arrays as they [behave strangely](http://stackoverflow.com/a/10253277/365496) — bames53, Nov 08 '12 at 19:04
The line where the function is called I get: '=' : cannot convert from 'double' to 'double [5]' The return line in the functions gives: 'return' : cannot convert from 'double [5]' to 'double' — user1810269, Nov 08 '12 at 19:08
Welcome on SO. Did you know that you can edit your own question to modify or add more information? Please have a look to our FAQ as well http://stackoverflow.com/faq. — ForceMagic, Nov 08 '12 at 19:20

score 3 · Accepted Answer · answered Nov 08 '12 at 18:59

3

One of your errors is from the fact that your function is declared to return a single double but you are attempting to return an array of doubles. So you either need to change your function heading to accomodate for that, or only return one double

Not related to the errors, but you should definitely initialize average to 0.0 when you start, otherwise you have undefined behavior in the calculation

answered Nov 08 '12 at 18:59

Dan F

17,654
5
72
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1

.. and `averages` can't really be returned from the function because they are local – Israel Unterman Nov 08 '12 at 19:00
I just need the averages of each row returned by the function as a vector but have no idea how. – user1810269 Nov 08 '12 at 19:03
@user1810269, bames53's link in your original question contains helpful information aso to how you should change your code to avoid errors and have well defined behavior – Dan F Nov 08 '12 at 19:08
How can I just make averages a non-local array. – user1810269 Nov 08 '12 at 19:17
Do not do that. Learn instead! – Yakk - Adam Nevraumont Nov 08 '12 at 20:53

C++ 2D array function

1 Answers1