sum of each diagonal in a matrix

Question

(incorrect output)

how can I find the sum of the primary and secondary diagonal in a matrix?

https://code.sololearn.com/ckGB4h7nh1Cg/#java

Answer 1

For sum of diagonals of square matrices, this will do

public class MatrixDiagonalSum
{
public static void main(String[] args)
{
int[][] matrix =
{
{ 1, 2, 3 },
{ 10, 20, 30 },
{ 100, 200, 300 }
};
int diagSum1 = 0, diagSum2 = 0;
int size = 3, index1 = 0, index2 = size;
for( int row = 0; row < size; row++ )
{
diagSum1 += matrix[ row ][ index1++ ];
diagSum2 += matrix[ row ][ --index2 ];
}
System.out.println( diagSum1 + "\n" + diagSum2 );
}
}

Answer 2

Eyy, for diagonal sum in your code
move declaratoon Pd, Sd before first for()
add parentheses to second for()
so second if() is included in second for()
move end of first for() before result display

public static void computeSumDia(
int[][] num, int[] sum) {
int Pd = 0, Sd = 0; //moved here

for (int row = 0; row < num.length; row++) {
//int Pd = 0, Sd = 0; //move up
int col;

for (col = 0; col < num[row].length; col++)
{ //parenthesis
if (row == col)
Pd += num[row][col];

if ((row + col) == (num.length - 1))
Sd += num[row][col];
} //parenthesis
} //parenthesis

System.out.println( ...

// } //deleted
}
}