如何乘以多维数组中的行和列？

Question

I need to multiply numbers in rows and in columns using nested for loops.

I have a sum of column, and I'm trying to use the same logic for multiplying rows but without any success...

$nxmArr = array(array());

$rows = 4;
$cols = 4;

$m = 0;

$colSum = 0;
$rowSum = 0;

for($i = 0; $i < $rows; $i++) {
  $colSum = 1;
  for($j = 0; $j < $cols; $j++) {
    $m++;
    $colSum *= $m;
    echo "$m ";
  }
  echo "Column Sum: $colSum<br>";
}

I have a list of numbers from 1 to 16, and I'm getting right results for every column, but when I try with rows I'm not getting right results...

Answer 1

The difficulty is that you are not adding up values from the matrix, you are just calculating the value in each column as you go along (the value $m ).

This sets the values in the first set of loops and sets the values, then does the calculations using these values

$rows = 4;
$cols = 4;
$nxmArr = [];
$value = 1;
for ( $row = 0; $row < $rows; $row++ )  {
    for ( $col = 0; $col < $cols; $col++ )  {
        $nxmArr[$row][$col] = $value++;
    }
}

// Start with rows...
for ( $row = 0; $row < $rows; $row++ )  {
    $rowSum = 1;
    // For each column
    for ( $col = 0; $col < $cols; $col++ )  {
        echo $nxmArr[$row][$col]." ";
        $rowSum *= $nxmArr[$row][$col];
    }
    echo " sum-".$rowSum.PHP_EOL;
}
/* Generates
1 2 3 4  sum-24
5 6 7 8  sum-1680
9 10 11 12  sum-11880
13 14 15 16  sum-43680
*/
// Then columns
for ( $col = 0; $col < $cols; $col++ )  {
    $colSum = 1;
    for ( $row = 0; $row < $rows; $row++ )  {
        echo $nxmArr[$row][$col]." ";
        $colSum *= $nxmArr[$row][$col];
    }
    echo " sum-".$colSum.PHP_EOL;
}
/* Generates
1 5 9 13  sum-585
2 6 10 14  sum-1680
3 7 11 15  sum-3465
4 8 12 16  sum-6144
 */