PHP - Indexed Array

In PHP, the array elements may be a collection of key-value pairs or it may contain values only. If the array consists of values only, it is said to be an indexed array, as each element is identified by an incrementing index, starting with “0”.

Creating an Indexed Array

An indexed array in PHP may be created either by using the array() function or with the square bracketsyntax.

$arr1 = array("a", 10, 9.99, true);
$arr2 = ["a", 10, 9.99, true];

Structure of an Indexed Array

Each element in the array has a positional index, the first element being at index “0”. The var_dump() function reveals the structured information of these arrays as −

array(4) {
  [0]=>
  string(1) "a"
  [1]=>
  int(10)
  [2]=>
  float(9.99)
  [3]=>
  bool(true)
}

We can use the index to traverse the array, fetch the value at a given index or modify the value of an element in place.

Traversing an Indexed Array in PHP

Any type of PHP loop can be employed to traverse an array. If we want to use afororwhileloop, we have to find the number of elements in the array with count() function and use its value as the test condition for the countedfororwhileloop.

Example

The following code uses aforloop to list all the elements in an indexed array.

<?php
   $numbers = array(10, 20, 30, 40, 50);

   for ($i=0; $i<count($numbers); $i++){
      echo "numbers[$i] = $numbers[$i] \n";
   }
?>

It will produce the followingoutput−

numbers[0] = 10
numbers[1] = 20
numbers[2] = 30
numbers[3] = 40
numbers[4] = 50

You can also use awhileordo-whileloop to traverse an indexed array. Here too, we need to find the array length with count() function.

Example

The following code traverses the given indexed array in reverse order −

<?php
   $numbers = array(10, 20, 30, 40, 50);
   $i = count($numbers)-1;
   while ($i>=0){
      echo "numbers[$i] = $numbers[$i] \n";
      $i--;
   }
?>

It will produce the followingoutput−

numbers[4] = 50
numbers[3] = 40
numbers[2] = 30
numbers[1] = 20
numbers[0] = 10

Accessing the Array Elements Using Index

You can access any value from an array using thearray[index]syntax. The value at a specific index may be assigned with a new value. The array is thus modified in place.

Example

The following program fetches the values from an array$arr1and places them in$arr2in the reverse order. So the value at 0th position in $arr1 becomes the last value in $arr2.

<?php
   $arr1 = array(10, 20, 30, 40, 50);
   $size = count($arr1);

   for ($i=0; $i<$size; $i++){
      $arr2[$size-$i-1] = $arr1[$i];
   }

   for ($i=0; $i<$size; $i++){
      echo "arr1[$i] = $$arr1[$i] arr2[$i] = $$arr2[$i] \n";
   }
?>

It will produce the followingoutput−

arr1[0] = $10 arr2[0] = $50
arr1[1] = $20 arr2[1] = $40
arr1[2] = $30 arr2[2] = $30
arr1[3] = $40 arr2[3] = $20
arr1[4] = $50 arr2[4] = $10

Traversing an Indexed Array Using “foreach” Loop

You can also use theforeachloop to iterate through an indexed array. Take a look at the followingexample−

<?php
   $arr1 = [10, 20, 30, 40, 50];
   foreach ($arr1 as $val){
      echo "$val \n";
   } 
?>

It will produce the followingoutput−

10 
20 
30 
40 
50

Note that PHP internally treats the indexed array as an associative array, with the index being treated as the key. This fact can be verified by the var_dump() output of the array.

Example

We can unpack each element of an indexed array in the key and value variables withforeachsyntax −

<?php
   $arr1 = [10, 20, 30, 40, 50];
   foreach ($arr1 as $key => $val){
      echo "arr1[$key] = $val \n";
   }
?>

It will produce the followingoutput−

arr1[0] = 10
arr1[1] = 20
arr1[2] = 30
arr1[3] = 40
arr1[4] = 50

In PHP, an array may be a mix of only values and key-value pairs. PHP assigns the index only to the values without keys.

Example

In this example, PHP assigns incrementing index to the numbers, skipping the key-value pair appearing in it.

<?php
   $arr1 = [10, 20, 
         "vals" => ["ten", "twenty"],
         30, 40, 50];

   var_dump($arr1);
?>

It will produce the followingoutput−

array(6) {
  [0]=>
  int(10)
  [1]=>
  int(20)
  ["vals"]=>
  array(2) {
    [0]=>
    string(3) "ten"
    [1]=>
    string(6) "twenty"
  }
  [2]=>
  int(30)
  [3]=>
  int(40)
  [4]=>
  int(50)
}

Properties of Indexed Arrays

Here are some of the properties of the indexed arrays are listed −

• The initial element has an index of zero and grows sequentially.
• An indexed array can store a wide range of values, like texts, numbers, floats and booleans.
• Arrays in PHP can grow and decrease dynamically without being explicitly declared.
• Indexed arrays can be easily looped using for or foreach loops.
• PHP has several built-in functions for managing indexed arrays, like count($arr), array_push($arr, “Value”), and array_pop($arr).