Example: Decimal to Binary Conversion using Recursion in Java

// Decimal to Binary Conversion using Recursion in Java
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {

    // Recursive function to convert decimal to binary
    public static String toBinaryRecursive(int decimal) {
        // Base case: if the decimal number is 0, its binary is "0"
        if (decimal == 0) {
            return "0";
        }
        // Base case: if the decimal number is 1, its binary is "1"
        if (decimal == 1) {
            return "1";
        }

        // Recursive step:
        // Get the remainder when divided by 2 (this is the current binary digit)
        int remainder = decimal % 2;
        // Recursively call the function with the quotient (decimal / 2)
        // and prepend the current remainder to the result
        return toBinaryRecursive(decimal / 2) + remainder;
    }

    public static void main(String[] args) {
        // Step 1: Create a Scanner object to read user input
        Scanner scanner = new Scanner(System.in);

        // Step 2: Prompt the user to enter a decimal number
        System.out.print("Enter a non-negative decimal number: ");
        int decimalNumber = scanner.nextInt();

        // Step 3: Validate input to ensure it's non-negative
        if (decimalNumber < 0) {
            System.out.println("Please enter a non-negative number.");
        } else {
            // Step 4: Call the recursive function to convert the number
            String binaryRepresentation = toBinaryRecursive(decimalNumber);

            // Step 5: Handle the special case for input 0, as our base case for 0 returns "0"
            // but for other numbers, it builds up. This ensures "0" is correctly handled.
            if (decimalNumber == 0) {
                System.out.println("Binary representation: 0");
            } else {
                System.out.println("Binary representation: " + binaryRepresentation);
            }
        }

        // Step 6: Close the scanner
        scanner.close();
    }
}