Arrays and Iteration

Indexed Lookup

An indexed array lookup reads one value by its zero-based position.

index An index is the numeric position used to choose a value from an array.

Indexed Lookup

index
indexed_lookup.php
Replay: real traced execution (multi-file project)
<?php
$index = 1;
$value = [4, 8, 12][$index];
$doubled = $value * 2;

echo "index=" . $index . "\n";
echo "value=" . $value . "\n";
echo "doubled=" . $doubled . "\n";

<?php
$index = 0;
$value = [4, 8, 12][$index];
$doubled = $value * 2;

echo "index=" . $index . "\n";
echo "value=" . $value . "\n";
echo "doubled=" . $doubled . "\n";

<?php
$index = 2;
$value = [4, 8, 12][$index];
$doubled = $value * 2;

echo "index=" . $index . "\n";
echo "value=" . $value . "\n";
echo "doubled=" . $doubled . "\n";

  1. $index ← 1, $value ← 8, $doubled ← 16

    1<?php2$index→ 1 = 1; //@index=0, 23$value→ 8 = [4, 8, 12][$index]8;4$doubled→ 16 = $value8 * 2;56echo "index=" . $index1 . "\n";7echo "value=" . $value8 . "\n";8echo "doubled=" . $doubled16 . "\n";
    outputindex=1
value=8
doubled=16

  1. $index ← 0, $value ← 4, $doubled ← 8

    1<?php2$index→ 0 = 0;3$value→ 4 = [4, 8, 12][$index]4;4$doubled→ 8 = $value4 * 2;56echo "index=" . $index0 . "\n";7echo "value=" . $value4 . "\n";8echo "doubled=" . $doubled8 . "\n";
    outputindex=0
value=4
doubled=8

  1. $index ← 2, $value ← 12, $doubled ← 24

    1<?php2$index→ 2 = 2;3$value→ 12 = [4, 8, 12][$index]12;4$doubled→ 24 = $value12 * 2;56echo "index=" . $index2 . "\n";7echo "value=" . $value12 . "\n";8echo "doubled=" . $doubled24 . "\n";
    outputindex=2
value=12
doubled=24