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]'"

• Dan F: On which lines are you getting the errors?
• bames53: You should avoid raw arrays as they behave strangely
• user1810269: 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'
• ForceMagic: 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.

Answer 1

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

• Israel Unterman: .. and averages can't really be returned from the function because they are local
• user1810269: I just need the averages of each row returned by the function as a vector but have no idea how.
• Dan F: @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: How can I just make averages a non-local array.
• Yakk - Adam Nevraumont: Do not do that. Learn instead!