The decoct() function in PHP is used to convert a decimal (base 10) number into its octal (base 8) representation. This function is useful in applications that require octal numbers, such as permissions in Unix-like operating systems.

Syntax:

decoct(int $number): string

• $number: The decimal number to be converted. This must be an integer.
• Return Value: Returns the octal representation of the given decimal number as a string.

Example 1: Basic Usage

<?php
echo decoct(8);
?>

Output:

10

Explanation: The decimal number 8 is converted to its octal equivalent, which is 10 in base 8.

Example 2: Conversion of Larger Numbers

<?php
echo decoct(64);
?>

Output:

100

Explanation: The decimal number 64 is represented in octal as 100, since $8^2 = 64$.

Example 3: Conversion of Odd Numbers

<?php
echo decoct(17);
?>

Output:

21

Explanation: The decimal number 17 converts to 21 in octal (1 * 8^1 + 1 * 8^0 = 16 + 1 = 17).

Example 4: Zero

<?php
echo decoct(0);
?>

Output:

0

Explanation: The octal representation of 0 is simply 0.

Key Points:

• Input Type: The input for decoct() must be an integer. If a non-integer value is provided, it will be converted to an integer.
• Negative Numbers: The function does not throw an error for negative numbers; however, the octal representation is typically not defined for negative values. It will convert it to its absolute value.
• Use Cases: This function is useful in file permission settings in Unix/Linux environments, where permissions are often expressed in octal format.

Example of Practical Use:

<?php
$filePermissions = 755; // Common permission setting in octal
$octalPermissions = decoct($filePermissions);
echo "The octal representation of file permissions $filePermissions is: $octalPermissions\n";

// Example of using in a loop
for ($i = 0; $i <= 10; $i++) {
    echo "Decimal: $i => Octal: " . decoct($i) . "\n";
}
?>

Output:

The octal representation of file permissions 755 is: 1367
Decimal: 0 => Octal: 0
Decimal: 1 => Octal: 1
Decimal: 2 => Octal: 2
Decimal: 3 => Octal: 3
Decimal: 4 => Octal: 4
Decimal: 5 => Octal: 5
Decimal: 6 => Octal: 6
Decimal: 7 => Octal: 7
Decimal: 8 => Octal: 10
Decimal: 9 => Octal: 11
Decimal: 10 => Octal: 12

Explanation: This example demonstrates how to convert a decimal number to its octal representation and shows how the decoct() function can be used in a loop to display octal equivalents for numbers from 0 to 10.

In summary, decoct() is a helpful PHP function for converting decimal numbers into octal format, making it useful for applications that involve octal number systems, such as file permissions in Unix-like operating systems.