Problems creating an ascii box with for-loops and if statements - php

Question

In this exercise I am trying to create a box with for-loops and if statements. I am stuck and not sure which part of my code is wrong. Somehow the $aboxwidth values 1 and 4 get repeated twice.
When substituting spaces for 0 the output looks like this:
output:
+0-0-0+0
|000|0
|000|0
+0-0-0+0
code:
<?php
//box builder
$iboxheight=4;
$aboxwidth=4;
// +-----------+
// | |
// | |
// | |
// +-----------+
// +--+
// | |
// | |
// +--+
//building boxheight
for ($i=1; $i <= $iboxheight; $i++) {
//$boxwidth
for ($a=1; $a <= $aboxwidth; $a++) {
//build + in corners
if (($i === 1 && $a === 1) || //corner top left
($i === 1 && $a === $aboxwidth) || // corner top right
($i === $iboxheight && $a === 1) || // corner bottom left
($i === $iboxheight && $a === $aboxwidth)) { // corner bottom right
echo "+";
}
//build top and bottom
if ($i === 1 || $i === $iboxheight) {
if ($a !== 1 && $a !== $aboxwidth) {
echo "-";
}
}
//build walls
if ($a === 1 || $a === $aboxwidth) {
if ($i !== 1 && $i !== $iboxheight) {
echo "|";
}
}
if ($i !== 1 || $i !== $iboxheight) {
if ($a !== 1 || $a !== $aboxwidth) {
echo "0";
// echo " ";
}
}
}
echo "<br>";
}
I am grateful for any tips and suggestions.
Thanks

Answer 1

The program will echo "0"; for every $i and $a. Why is that?
This ($i !== 1 || $i !== $iboxheight) is always true. And this $a !== 1 || $a !== $aboxwidth is always true. When $i is 1, it is not equal $iboxheight, therefore true. When $a is 1, it is not equal $aboxwidth, therefore true. And so on. The program echo's 0 for every iteration.
(You might try echo "($i,$a)"; in place of echo "0"; to see it in action).
If the || are changed to && it would accomplish the desired result, ie only echo {whatever} when the (row,column) is not on the "border".