Add diagonal of 2 dimensional array in Objective C - ios

Question

Given: 2 dimensional array :
[[1 2 3]
[4 5 6]
[9 8 9 ]]
Need to add diagonal of the array : 1+5+9 = 15
NSMutableArray *array = [NSMutableArray arrayWithObjects:[NSMutableArray arrayWithObjects:#1,#2,#3,nil],
[NSMutableArray arrayWithObjects:#4,#5,#6,nil],
[NSMutableArray arrayWithObjects:#9,#8,#9,nil],nil];
NSNumber* total = 0;
for (NSNumber* row in array) {
total = total + array[row][row];
}
NSLog(#"%#",total);
Here I can't access the element of the array. It gives error on "array[row][row]". What is the best way to initialize a 2D array and access the element of the array in Objective-C?

Answer 1

In your code, what you are doing here: for (NSNumber* row in array) is putting each element of array, inside the row variable (this is called array enumeration btw).
What you need is to use the index of the array - not the value of each element (that's what you are doing above).
Also, you don't have to use an object (NSNumber *) for your calculations. A simple NSInteger will do.
Here's the code:
NSMutableArray *array = [NSMutableArray arrayWithObjects:[NSMutableArray arrayWithObjects:#1,#2,#3,nil],
[NSMutableArray arrayWithObjects:#4,#5,#6,nil],
[NSMutableArray arrayWithObjects:#9,#8,#9,nil],nil];
NSInteger total = 0;
for (NSUInteger row = 0; row < array.count; row ++) {
total = total + [array[row][row] integerValue]; // integerValue converts the NSNumber to an NSInteger
}
NSLog(#"%d",total);