Summing a jagged int array in C#

Question

As done here: C # Two-dimensional int array,Sum off all elements , but this time with jagged arrays. Getting:

System.IndexOutOfRangeException.

I am a beginner asking for help. This is my code:

public static int Sum(int[][] arr) 
{
    int total = 0;
    for (int i = 0; i < arr.GetLength(0); i++)
    {
         for (int j = 0; j < arr.GetLength(1); j++) 
         { 
              total += arr[i][j];
         }
    } 
    return total; 
}

static void Main(string[] args)
{
     int[][] arr = new int[][] 
     {
          new int [] {1},
          new int [] {1,3,-5},
     };
     int total = Sum(arr);
     Console.WriteLine();
     Console.ReadKey();    
}

Answer 1

In your inner loop do this instead:

for (int i = 0; i < arr.Length; i++)
{
    if (arr[i] != null)
    {
        for (int j = 0; j < arr[i].Length; j++) 
        { 
            total += arr[i][j];
        }  
    }
} 
return total; 

Because your lists aren't even you get the exception on arr.GetLength(1) for the first dimension - it has no item at that place.

The if (arr[i] != null) line is needed in the case the array would look something like:

 int[][] arr = new int[][] 
 {
      new int [] {1},
      null,
      new int [] {1,3,-5},
 };

In this case, when we loop with i==1 and try to do arr[i].Length (meaning arr[1].Length we will recieve a NullReferenceException .

---

And after you do the basics and get to Linq all your current Sum method can be replaced with:

arr.SelectMany(item => item).Sum()

But it is good to start with the basics :)

Answer 2

Since you're using a jagged array the dimensions of that array aren't necessarily even. Have a look at the initialization code of that jagged array:

int[][] arr = new int[][] {
    new int [] {1},
    new int [] {1,3,-5},
};

So in the first dimension, there are two elements ( {1} and {1, 3, -5} ). But the second dimension isn't of the same length. The first element has got only one element ( {1} ) whereas the second element's got 3 elements ( {1, 3, -5} ). That's why you're facing the IndexOutOfRangeException .

To fix that, you'll have to adjust the inner loop to the number of elements for that dimension. You can do that like this:

for (int i = 0; i < arr.Length; i++) {
    for (int j = 0; j < arr[i].Length; j++) { 
        total += arr[i][j];
    }  
}