Egypt Secondary 3 Communication Technology, Week 12: The OR gate on a web page: the || test

The OR gate on a web page: the || test

ICT Secondary 3 Term 1, Unit 2, Topics 5–6: pp. 48–64

GoalWrite the OR test in PHP with ||, trace the page, and find the fault of a page where && and || were swapped.

New words

|| · PHP’s OR for conditions: true when at least one side is true| · a different operator that works on the bits of whole numbers, for example 6 | 3 is 7swapped operator · the fault of writing || where && belongs, or the other way roundrows that differ · the choices for which two versions of a rule give different results

Explanation

The OR page is the page of Week 10 with one change. The form is the same: two drop-down lists list1 and list2 and an Apply button. The PHP is the same too, and only the test inside the if is new: $choice1 == "on" || $choice2 == "on". The sign || is PHP’s OR for conditions. It is true when at least one side is true, as in the truth table of Week 11. A single | is another operator: it works on the bits of whole numbers, so 6 | 3 gives 7. For conditions write ||. The book prints no code for this page, so the function below is our own version, with the safer checks of Week 10. Now think about faults. If someone writes && on the OR page, or || on the AND page, the lamp is right for off, off and for on, on, but wrong for the two choices where the lists differ. Those two rows tell you which version you are looking at.

	AND page	OR page
the test	$a == "on" && $b == "on"	$a == "on" \|\| $b == "on"
lit for	on, on only	every choice except off, off
unlit for	three choices	off, off only

Worked examples

Php

1function lamp(array $post): string {
2    $allowed = ["on", "off"];
3    $first = "off";
4    $second = "off";
5    $state = "unlit";
6    if (isset($post['apply'])) {
7        $first = in_array($post['list1'] ?? "", $allowed, true) ? $post['list1'] : "off";
8        $second = in_array($post['list2'] ?? "", $allowed, true) ? $post['list2'] : "off";
9        $state = ($first === "on" || $second === "on") ? "lit" : "unlit";
10    }
11    return "$first $second $state";
12}
13
14echo lamp([]), "\n";
15echo lamp(['apply' => 'Apply', 'list1' => 'off', 'list2' => 'on']), "\n";
16echo lamp(['apply' => 'Apply', 'list1' => 'off', 'list2' => 'off']), "\n";
17echo lamp(['apply' => 'Apply', 'list1' => 'maybe', 'list2' => 'on']);

Output

off off unlit
off on lit
off off unlit
off on lit

The OR page as a function, with the safer checks of Week 10. The output lines are for a first visit, off and on, off and off, and the text maybe with on.

Php

1var_dump(true || false);
2var_dump(false || false);
3var_dump(1 | 0);
4var_dump(6 | 3);

Output

bool(true)
bool(false)
int(1)
int(7)

The signs || and | on their own.

list1	list2	AND test	OR test
off	off	unlit	unlit
off	on	unlit	lit
on	off	unlit	lit
on	on	lit	lit

The swapped-operator fault. The two rows where the lists differ are the only rows that tell the versions apart.

Class activity

A page is meant to be an OR page, but its test is $choice1 == "on" && $choice2 == "on". For which of the four choices does it show the wrong lamp, and what does it show? Then write the corrected test.

Practice

What does || mean in PHP?

Which line differs between the AND page and the OR page?

What does 6 | 3 give, and why?

The OR page gets list1 = off and list2 = on. What does the lamp show?

The OR gate in VB.NET and PHP

The OR gate on a web page: the || test