Example: Decimal to Octal (Manual) in Java

// Decimal to Octal (Manual)
import java.util.Scanner;

// Main class containing the entry point of the program
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        // Step 1: Prompt user for a decimal number
        System.out.print("Enter a decimal number: ");
        int decimalNumber = scanner.nextInt();

        // Step 2: Initialize octal value and multiplier
        int octalNumber = 0;
        int i = 1; // Multiplier to place remainders at correct positions (1, 10, 100, etc.)
        int tempDecimalNumber = decimalNumber; // Use a temporary variable for calculation

        // Step 3: Loop until the decimal number becomes 0
        while (tempDecimalNumber != 0) {
            // Get the remainder when divided by 8
            int remainder = tempDecimalNumber % 8;

            // Add the remainder to the octal number, multiplied by its place value
            octalNumber += remainder * i;

            // Divide the decimal number by 8
            tempDecimalNumber /= 8;

            // Multiply 'i' by 10 to shift position for the next remainder
            i *= 10;
        }

        // Step 4: Display the result
        System.out.println("Octal equivalent: " + octalNumber);

        scanner.close();
    }
}