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]'"

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
– user1810269, Commented Nov 8, 2012 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 stackoverflow.com/faq. — ForceMagic
– ForceMagic, Commented Nov 8, 2012 at 19:20

Dan F · Accepted Answer · 2012-11-08 18:59:10Z

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 8, 2012 at 18:59

Dan F

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5 Comments

Israel Unterman Over a year ago

.. and averages can't really be returned from the function because they are local

user1810269 Over a year ago

I just need the averages of each row returned by the function as a vector but have no idea how.

Dan F Over a year ago

@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

user1810269 Over a year ago

How can I just make averages a non-local array.

Yakk - Adam Nevraumont Over a year ago

Do not do that. Learn instead!

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