PHP Program to Convert Decimal to Binary (Using Loop, Recursion, Bitwise, Built-in, and More)

Introduction

Binary numbers (composed of 0s and 1s) are the fundamental building blocks of digital systems. As a server-side scripting language, PHP can easily handle base conversions.

In this article, we will write 5+ different PHP programs to convert a decimal number to binary using loops, recursion, bitwise, and other approaches.

 

Problem Statement

Write multiple PHP programs to convert a decimal number into binary using various logic-based and built-in methods.

 

Use Cases

• For educational tools and online compilers

• Backend scripts handling IP/binary flags

• Logical problem-solving for students learning PHP

• Building number system converters in web apps

 

Method 1: Using While Loop with String Concatenation

<!-- Program 1: Convert Decimal to Binary using While Loop -->
<?php
function decimalToBinaryLoop($number) {
    if ($number == 0) return "0";
    $binary = "";
    while ($number > 0) {
        $binary = ($number % 2) . $binary;
        $number = intdiv($number, 2);
    }
    return $binary;
}

echo "Binary (34): " . decimalToBinaryLoop(34);
?>

 

Explanation

1. Start with an empty binary string.

2. Divide the number by 2 repeatedly.

3. Store each remainder (0 or 1) from right to left.

Output

 

Method 2: Using Recursion

<!-- Program 2: Convert Decimal to Binary using Recursion -->
<?php
function decimalToBinaryRecursive($number) {
    if ($number == 0) return "";
    return decimalToBinaryRecursive(intdiv($number, 2)) . ($number % 2);
}

$result = decimalToBinaryRecursive(15);
echo "\nBinary (15): " . ($result === "" ? "0" : $result);
?>

 

Explanation

1. The function calls itself until the number is 0.

2. On return, the remainder is appended to the binary result.

3. Base case: return empty string for 0.

Output

 

Method 3: Using Bitwise Operators

<!-- Program 3: Convert Decimal to Binary using Bitwise -->
<?php
function decimalToBinaryBitwise($number) {
    $binary = "";
    $started = false;
    for ($i = 31; $i >= 0; $i--) {
        $bit = ($number >> $i) & 1;
        if ($bit == 1) $started = true;
        if ($started) $binary .= $bit;
    }
    return $binary === "" ? "0" : $binary;
}

echo "\nBinary (29): " . decimalToBinaryBitwise(29);
?>

 

Explanation

1. Shift number right by i bits.

2. Use bitwise AND with 1 to extract the current bit.

3. Skip leading zeros until the first 1.

Output

 

Method 4: Using PHP Built-in decbin() Function

<!-- Program 4: Convert Decimal to Binary using Built-in Function -->
<?php
$number = 20;
echo "\nBinary (20): " . decbin($number);
?>

 

Explanation

1. decbin() is a built-in PHP function.

2. It converts any decimal number directly to a binary string.

Output

 

Method 5: Stack Logic with Array

<!-- Program 5: Convert Decimal to Binary using Array Stack Simulation -->
<?php
function decimalToBinaryStack($number) {
    if ($number == 0) return "0";
    $stack = array();
    while ($number > 0) {
        array_push($stack, $number % 2);
        $number = intdiv($number, 2);
    }
    return implode('', array_reverse($stack));
}

echo "\nBinary (39): " . decimalToBinaryStack(39);
?>

 

Explanation

1. Simulate stack using array_push().

2. Push all remainders.

3. Reverse and join the binary digits.

Output

 

Method 6: Manual Left Padding Logic

<!-- Program 6: Convert Decimal to Binary using Left Padding -->
<?php
function decimalToBinaryManual($number) {
    if ($number == 0) return "0";
    $binary = "";
    while ($number > 0) {
        $bit = $number % 2;
        $binary = $bit . $binary;
        $number = intdiv($number, 2);
    }
    return str_pad($binary, 8, "0", STR_PAD_LEFT);  // Optional padding
}

echo "\nBinary (9): " . decimalToBinaryManual(9);
?>

 

Explanation

1. Prepend binary digits manually.

2. Optionally, pad with leading 0s to 8-bit format using str_pad.

Output

 

Conclusion

You now have a collection of 6 different PHP programs to perform decimal to binary conversion using loops, recursion, bitwise logic, arrays, and PHP’s built-in tools. This approach improves logical thinking and also teaches PHP's strengths in control flow and data manipulation.