Summing a 2D array in c

Question

   void ArrayDiagonal(double Array[4][4])
{
    //declare local variables//
    int i,j=0;
    double dSum = 0;
    for(i=0;i<4;i++)
        {
            for(j=0;j<4;j++)
            {
                if(i==j)
                {
                    dSum=dSum+Array[i][j];
                }
            }
        }
    printf("The sum of the main diagonal elements is = %.2f\n", dSum);
    OffArrayDiagonal(Array);
}

void OffArrayDiagonal(double Array[4][4])
{
    //declare local variables//
    int i,j=0;
    double dOff= 0;
    for(i=0;i<4;i++)
        {
            for(j=4;j=0;j++)
            {
                if(i==j)
                {
                    dOff=dOff+Array[i][j];
                }
            }
        }
    printf("The sum of the off diagonal elemets is   = %.2f\n", dOff);
}

So for a project i'm doing I have to add the diagonal elements of the array together. The first function work properly but I cant get the other direction to work properly. Any ideas?

Answer 1

One problem is that j starts at 4 and then increments (increases) to 5, 6, ... You also want to start at 3 instead of 4. And you don't want to assign anything to j in the conditional. So use for(j=3;j>=0;j--).

You don't really need a two-dimensional iteration though, since the diagonal is one-dimensional. So a simpler and more efficient solution would be

for (i = 0 ; i < 4 ; i++)
    dOff += Array[i][3-i];

and similarly for the first diagonal.