Control structures and arrays: if/else/elseif/switch; for, while, do-while, foreach; arrays (indexed, associative, multidimensional); array operations (sort(), asort(), ksort(), array_merge())

📖 Theory

The registration list is an array

The event portal's core data is a LIST: everyone registered for Garba Night. In PHP that list is an array, and PHP's arrays are unusually powerful: they can be simple numbered lists, or maps from keys to values, or nested tables of records.

Control flow (if, switch, loops) you already know from 5 languages; PHP's versions hold few surprises. So this lesson spends its energy where PHP is genuinely distinctive and exam-heavy: arrays, the loop that walks them (foreach), and the family of functions that sort and reshape them.

📖 Theory

Control flow, briefly

PHP's control structures are the familiar set:

• if / elseif / else and switch (with break per case) for decisions
• for, while, do-while for counted and conditional loops
• foreach for walking arrays: the one worth real attention

foreach comes in 2 forms: foreach ($arr as $value) to visit each value, and foreach ($arr as $key => $value) to visit each key AND its value. For associative arrays (below), the second form is essential.

📖 Theory

Three kinds of array

PHP arrays come in 3 shapes:

• Indexed: numeric keys from 0. $names = ["Riya", "Aman"]; so $names[0] is "Riya"
• Associative: STRING keys mapping to values. $event = ["seats" => 350, "venue" => "Ground"]; so $event["seats"] is 350
• Multidimensional: arrays of arrays, perfect for a table of records: a registration list where each entry is itself an associative array of one person's details

The associative array is PHP's signature strength: a built-in map (like a dictionary) with clean key => value syntax.

⌨️ Practical

Arrays and foreach (predict the output)

<?php
  // Associative array: keys map to values
  $event = ["venue" => "Ground", "seats" => 350, "fee" => 50];

  foreach ($event as $key => $value) {
    echo "$key = $value <br>";
  }
  // venue = Ground
  // seats = 350
  // fee = 50

  // Multidimensional: a registration list
  $regs = [
    ["name" => "Riya", "paid" => true],
    ["name" => "Aman", "paid" => false],
  ];
  echo $regs[0]["name"];   // Riya
  echo count($regs);        // 2
?>

📊 At a glance

The sorting family (the exam favourite)

🧩 Quiz

You have an associative array $scores = ["Riya"=>80, "Aman"=>95]. You want to sort by score BUT keep each name attached to its score. Which function?

1. sort(): it sorts the values
2. asort(): it sorts by value while keeping the key => value association
3. ksort(): it sorts by key
4. array_merge(): it combines arrays

💭 Think first

sort() destroyed the map

A student runs sort() on the $scores associative array to order by score, then loops with foreach($scores as $name => $score). The names come out as 0 and 1, not Riya and Aman. Explain what happened, then tap.

⚠️ Watch out

Array traps

sort() on associative arrays: it destroys the keys; use asort() to keep them.

foreach without key => value: on an associative array you need as $key => $value to see the keys.

Off-by-one on count(): count() gives the number of elements; the last index is count() - 1 for indexed arrays.

Undefined keys: accessing $arr["missing"] warns and gives null; check with isset() first.

Modifying an array while foreaching it: can cause subtle bugs; build a new array instead.

📖 Theory

Data and logic done; now real input

The portal can now store its registration list as a multidimensional array, walk it with foreach, and sort it any way needed. But the data has to come from somewhere: a user filling a FORM. The next lesson connects HTML forms to PHP with $_GET and $_POST, wraps repeated logic in FUNCTIONS, and adds the input validation and sanitization every real login form requires. Unit 1 ends where the portal comes alive: handling a real registration.

✅ Summary

Key takeaways

• Control flow is familiar: if/elseif/else, switch (with break), for, while, do-while, and foreach for arrays.
• foreach walks arrays: as $value for values, as $key => $value for key-value pairs.
• Three array kinds: indexed (numeric keys from 0), associative (string key => value), multidimensional (arrays of arrays).
• Associative arrays are PHP's built-in maps; multidimensional arrays model tables of records (the registration list).
• Sorting: sort() orders values but RE-INDEXES (loses keys); asort() keeps key-value pairs; ksort() sorts by key.
• Choose the sort function by whether you must preserve keys.
• Memory hook: sort loses keys, asort keeps them.