outputs an addition and multiplication table for kids that is shorter to memorize because it doesn't have repeated values

plus_times_table.php

#!/usr/bin/php
<?php

error_reporting(E_ALL);
ini_set('display_errors', '1');

# outputs an addition table for kids that is shorter to memorize because
# it doesn't have repeated values
function fill(&$table, $x, $sign, $y) {
    $min = min($x, $y);
    $max = max($x, $y);
    if (isset($table[$min][$max])) {
        return;
    }
    if ($sign == '+') {
      $table[$min][$max] = ($min + $max);
    } else if ($sign == '*') {
      $table[$min][$max] = ($min * $max);
    } else {
      die("invalid sign: $sign");
    }
}

function dump($table, $sign = '+') {
    foreach ($table as $x => $list) {
        foreach ($list as $y => $value) {
            print "{$x}{$sign}{$y}={$value}\n";
        }
        echo "\n";
    }
}

foreach (['*', '+'] as $sign) {
  $table = array();
  for ($x = 1; $x <= 10; $x++) {
      for ($y = 1; $y <= 10; $y++) {
          fill($table, $x, $sign, $y);
      }
  }
  dump($table, $sign);
}