PHP supports binary, octal, and hexadecimal number systems using specific prefixes and conversion functions. 1. Binary numbers are prefixed with 0b (e.g., 0b1010 = 10 in decimal). 2. Octal numbers use 0 or 0o (e.g., 012 or 0o12 = 10 in decimal). 3. Hexadecimal numbers use 0x (e.g., 0xA = 10 in decimal). 4. Use decbin() and bindec() to convert between decimal and binary. 5. Use decoct() and octdec() for decimal-octal conversions. 6. Use dechex() and hexdec() for decimal-hexadecimal conversions. 7. Use intval($string, $base) to safely convert strings from any base to decimal. 8. Be cautious with leading zeros in older PHP versions, as they indicate octal interpretation. 9. These systems are used in file permissions (octal), bitwise operations (binary), and color codes (hexadecimal). 10. Always validate input when handling string-based numbers to avoid unexpected behavior, as PHP’s conversion functions may ignore invalid characters or apply automatic interpretation. Proper use of prefixes and functions ensures accurate cross-base number handling in PHP.

When working with different number systems in PHP—like binary, octal, and hexadecimal—it’s important to understand how PHP interprets and converts these values. While PHP primarily works with decimal (base-10) numbers, it provides built-in functions and syntax to handle binary (base-2), octal (base-8), and hexadecimal (base-16) seamlessly.

How PHP Recognizes Different Number Bases

PHP allows you to define integers using different bases directly in code using specific prefixes:

• Binary (base-2): Prefix with 0b
  Example: 0b1010 → 10 in decimal
• Octal (base-8): Prefix with 0 or 0o (since PHP 8.1)
  Example: 012 or 0o12 → 10 in decimal
• Hexadecimal (base-16): Prefix with 0x
  Example: 0xA → 10 in decimal

echo 0b1010;   // Outputs: 10
echo 012;      // Outputs: 10
echo 0o12;     // Outputs: 10 (PHP 8.1 )
echo 0xA;      // Outputs: 10

?? Note: Older versions of PHP interpret a leading zero (e.g., 012) as octal. Be careful when parsing strings or user input with leading zeros.

Converting Numbers Between Bases

PHP provides several built-in functions to convert numbers between different bases.

1. decbin() and bindec() – Decimal to Binary and Back

• decbin($number) converts a decimal number to binary (returns a string).
• bindec($binaryString) converts a binary string back to decimal.

echo decbin(10);     // Outputs: 1010
echo bindec('1010'); // Outputs: 10

Note: bindec() ignores leading zeros and is case-insensitive for input.

2. decoct() and octdec() – Decimal to Octal and Back

• decoct($number) converts decimal to octal.
• octdec($octalString) converts octal string to decimal.

echo decoct(10);     // Outputs: 12
echo octdec('12');   // Outputs: 10

3. dechex() and hexdec() – Decimal to Hexadecimal and Back

• dechex($number) converts decimal to hexadecimal (lowercase).
• hexdec($hexString) converts hex string to decimal (ignores case and 0x prefix).

echo dechex(255);    // Outputs: ff
echo hexdec('FF');   // Outputs: 255
echo hexdec('0xFF'); // Also valid → 255

Note: hexdec() is forgiving—it skips non-hex characters like 0x, but be cautious with malformed input.

Practical Use Cases

These number systems are commonly used in:

• Permissions and file modes (octal):

  chmod('file.txt', 0644); // 0644 is octal

• Bitwise operations (binary):

  $flags = 0b1010 | 0b0110; // Bitwise OR

• Color codes and memory addresses (hexadecimal):

  $color = 0xFF5733; // Represents a color in RGB

Handling String Inputs and Edge Cases

When dealing with user input or strings, always validate and sanitize:

• Use intval($string, $base) to convert a string to an integer in a given base:

  intval('1010', 2);   // Binary string → 10
  intval('12', 8);     // Octal string → 10
  intval('A', 16);     // Hex string → 10

• This is safer than relying on automatic type conversion.

Also, be aware:

• Binary strings must contain only 0 and 1.
• Invalid octal digits (like 8 or 9) cause silent truncation or errors depending on context.
• Hex strings can include a-f or A-F.

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Summary of Key Functions

Conversion	Function
Decimal → Binary	decbin()
Binary → Decimal	bindec()
Decimal → Octal	decoct()
Octal → Decimal	octdec()
Decimal → Hex	dechex()
Hex → Decimal	hexdec()
Any base → Decimal	intval($str, $base)

Basically, PHP makes it straightforward to work across number systems—just use the right function or prefix. The key is knowing when to use each and being cautious with input formats.

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